stroke Dr. Dave's answers to frequently-asked questions
(FAQs),
mostly from the BD
CCB and AZB
discussion forums
maintained for the book: The
Illustrated Principles of Pool and Billiards,
the DVD series: The Video Encyclopedia of Pool Shots,
and the monthly Billiards
Digest "Illustrated Principles" instructional articles
for more information, see Section 2.05 in The Illustrated Principles of Pool and Billiards
How does the speed and acceleration of the cue vary during a typical stroke?
See: HSV B.40 - stroke speed and acceleration analysis, with Bob Jewett. Bob Jewett has an article with a good example plot (see page 9 here).
See also: TP B.4 - Stroke speed and acceleration vs. distance. Here is the summary from the analysis:
With typical pendulum (p) strokes, the speed is more constant (i.e., leveled-off) at CB impact, possibly making it easier to control shot speed, because the speed is less sensitive to variations in bridge and stroke length. With typical "accelerate into the ball" (a) strokes, the force increases and levels off during the stroke, and force is being applied all of the way up to ball impact. With a classic pendulum stroke, it is natural to coast into the ball with no force at impact. The peak force is typically lower with an "accelerate into the ball" stroke than with a pendulum stroke (for the same shot speed) because force is applied over a larger distance. Therefore, for some people, this type of stroke might seem to require less effort for a given speed, and higher speeds might be possible. A typical "accelerate into the ball" stroke usually involves more of a "piston-like" stroke, with shoulder motion and elbow drop, allowing some people to generate force more easily throughout the stroke. One disadvantage of a piston stroke is that tip-contact-point accuracy might be more difficult to control.
For more info on the effects of speed and acceleration, see: follow through.
TP A.9 - Cue accelerometer measurements shows accelerometer measurements and describes cue reactions during strokes and CB impacts. The blue curves in the top three plots (red curves in the bottom two plots) represent forward acceleration. A positive acceleration implies slowing in the backward direction (e.g., at the end of the back swing) and/or speeding up in the forward direction (e.g., during most of the pre-impact portion of the forward stroke). A negative acceleration implies slowing in the forward direction (e.g., in the later part of the forward warm up strokes) and/or speeding up in the backward direction (e.g., at the beginning of the backstroke).
I think the relatively flat portion of Andreas' curve, before impact, corresponds to the second half of his back-swing. Notice how it is nearly identical to the shapes in the warm-up strokes (which I think are fairly firm). I think the entire forward stroke, before impact, is represented by the tall peak. The final forward stroke is much faster and more forceful than the warm-up strokes. After the peak, and before impact, the acceleration appears to go negative a little, implying he was actually decelerating a little before impact (if you trust the sensor, its calibration, and the data acquisition). At impact, the signals go wild due to shock waves and vibration.
In the first two plots (softer strokes), the acceleration is still positive at impact, implying that the cue stick is speeding up during the entire forward stroke (e.g., he is accelerating into the ball). Both of Pizutto's plots show slight slowing (negative acceleration) just before impact.
Andreas does not appear to have a distinct pause at the transition between the back and forward stroke because the acceleration curve would be flat (at zero) if there were a deliberate pause.
The spike before impact represents the entire forward stroke, not any weird wrist action. Note that the time scales are very different between the two sets of plots. Pizutto's plots are just showing the final forward stroke and the resulting shock and vibration immediately after impact. Andreas' plots show a much large time interval, including warm-up strokes.
If I accelerate into the CB, will I get more "juice" on the ball?
from Jal:
In principle, the cueball will ... have more speed and spin ... when you apply a force during impact. It's just that since the impact period is so short (mainly), the effect is essentially negligible. If you had a really, really soft tip such that contact lasted, say, a second, that would be a different story. So would being able to apply something like 100 lbs of force, as opposed to what we actually apply, about 15-20 lbs at the peak of a power stroke (much less throughout most of the rest of the stroke).
That aside, "accelerating through" can, in theory, give you noticeably more ["juice"] by generating more cue speed before impact commences. One impact begins, virtually nothing short of a superhuman effort can alter things. And the term "accelerate through" is a misnomer. You can continue to apply force, but the impact will inevitably slow the cue down unless you can muster something on the order of 400 lbs.
[The cue] does sense force, but the force doesn't last long (it takes force acting over time to get things moving). And the entire force that you might be applying with your grip hand is not what the cueball sees; it's only about 1/4'th of that. The force that really gets its attention is the one generated by the impact of the already moving cue, and this can approach 300-500 lbs. That's why cue speed is important, not the relatively meager force generated by our stroking arm.
What are considered the "best practices" for stroke mechanics?
My stroke "best practices" document summarizes the generally-accepted technique advice. My fundamentals "best practices" check-sheet is also useful to help diagnose possible problems with mechanics. These and other useful documents can be found in the Instructor and Student Resources section of my website. Here's a basic demonstration of a classic pendulum stroke:
What are considered "best practices" for the stance?
from av84fun:
There is no such thing as an "ideal stance" for everyone. There is what I would call a "classic" stance...that which is recommended in most texts dealing with the subject which are, in turn, based on the stances used by a large number of top players.
That "classic stance" might be described as:
1. Placing the back foot on the extended line on which the CB will be directed toward the OB.
2. Place the front foot at about a 45 degree angle to that line.
3. Bend forward with a RELATIVELY straight back leg onto a bent forward leg.
4. Place the cue directly under the chin.
5. In the SET position, with the tip very close to the OB, the forearm should be at a right angle to the CUE.
The variations from "classic" are nearly endless but frequently would include.
1. Instead of a nearly straight rear leg, both legs are bent in a partial "squat" type of stance...watch Strickland who does this.
2. The Brits tend to adopt more of a snooker stance where the forward let is placed at a wider than 45 degree angle which, in turn, "squares up" the chest toward a more perpendicular orientation to the line toward the OB.
3. The chin is moved to various positions to the outside (away from the body) of centered under the chin.
Finally, various chin heights (above the cue) are used. Back in the day, the chin was help several inches above the cue but today, many pros have moved the chin much lower...Allison's cue rubs back and forth ON her chin.
from dr_dave:
The amount of leg spread
also varies a lot from one person to the next based on the person's height, flexibility,
chin height above the cue, body shape and anatomy, and comfort level. The photos
in my document are of a top regional player. I also prefer a wide foot stance
because of my height (6' 3") and desire to get my head low without too much
strain on my lower back and neck. As with most stance, grip, and bridge related
issues, individual comfort is a primary consideration.
What is the advantage of having a low stance with the chin close to the cue?
Having you eyes closer to the cue helps you more easily visualize the alignment of the cue with the desired aiming line. With your head low, it might help to use an open bridge (see Diagram 3 in my December '08 article) Most snooker players, who require tremendous accuracy, use an open bridge and have there chin just above (or even touching) the cue.
from Spiderman:
I find that my "chin height" varies with the shot. For shots where the CB and OB are a reasonable distance apart, I am fairly low on the cue. For cut shots with the OB close to the CB, my stance raises a little to facilitate visualizing the contact point and the alignment of the balls at contact. For straight-ins, I don't raise as much as for cuts.
elbow drop and pendulum stroke
Is it recommended to drop one's elbow during the stroke?
I think there is a lot of misunderstanding and misrepresentation in the "elbow drop" arena. But it is my understanding that the general "don't drop the elbow" advice is not as rigid as some people think. Obviously, for an extreme power shot, the elbow will want to drop naturally during the follow through (due to the momentum of the arm and stick). The problem lies with dropping the elbow when it is not intended, especially if the elbow is dropped before cue ball contact. For most (almost all) shots, and for most people (especially beginners), accuracy and consistency will be better if the elbow is not dropped before (or after) cue ball contact. The problem with dropping the elbow after cue ball contact (e.g., when it is not required based on shot power) is that if one's timing is a little off, the elbow might drop a little before contact, which can affect CB contact point accuracy.
Here are some good video demonstrations of a non-elbow-drop pendulum stroke:
Here's another with a power draw shot. Elbow drop and pendulum vs. piston stroke are also discussed in:
HSV B.40 - stroke speed and acceleration analysis, with Bob Jewett
An advantage of dropping the elbow during the stroke is it can allow more power by involving the shoulder muscles. Having a slightly "choked up" grip, where the forearm is forward of vertical at CB impact, and using a more upright stance can also help add power. Here's a good example of elbow-drop power draw from Mike Masse. Related discussion and demonstrations on how to add power to a break shot can be found here:
NV A.20 - Colin Colenso's power break instructional video
from Bob_Jewett:
...the vast majority of players drop their elbows some on power shots. When talking "elbow drop" you need to be clear about how much. Many players drop their elbows only about the thickness of their upper arm on most power shots.
Two articles that discuss elbows and the strange things people do with them are:
http://www.sfbilliards.com/articles/2004-02.pdf
http://www.sfbilliards.com/articles/2004-03.pdfFor most of the players I've checked, there are some shots for which their elbows do not move.
from pooltchr:
...the vast majority of students who come to me are looking for consistency. The best way to achieve this is SPF and no elbow drop. There are select shots where dropping the elbow may allow more power, but that same majority would be giving up a lot of accuracy to gain the power. In my opinion, accuracy is more critical than power. There are always going to be players at the top of the game who can control a full arm stroke with accuracy and consistency. They would be in the minority.
I have had very good success helping students improve their control by using the pendulum stroke. As an instructor, I have to consider each student as an individual, so I can't say I would ever say that a student MUST not drop their elbow. But so far, whenever I have had a student try the pendulum stroke, they have shown very quick improvement in accuracy. I have one student who uses this stroke on his break! He regularly makes something (often multiple balls) and almost always lands the cue ball in the center of the table. I don't see any reason to introduce a full arm swing to a player who would be better served from an accuracy standpoint by developing a simpler motion. When the student comes to me who can consistently make controlled contact with a full arm stroke, I don't think I would suggest any changes. Until that student appears, I think this is the best method to teach. There are going to be exceptions, but I suspect they are few and far between.
from Mike Page:
If you were to install webcams in a hundred poolrooms throughout the world and view 1000 random elbow drops on pool strokes, those 1000 strokes might be divvied up as follows:
990 strokes: category A elbow drops
9 strokes: category B elbow drops
1 stroke: category C elbow drop
category A elbow drops--
the vast majority of them--are plainly and simply bad mechanics. This person's elbow is moving during the stroke, as perhaps is his or her head, making strokes inconsistent, making strokes rely on carefully choreographed timing of different motions, and encouraging the addition of other compensating motions. These people absolutely will benefit from learning good mechanics like those Randy and Scott and Steve and others advocate so well. These people should heed the advice of instructors like those I just mentioned and practice it until one nipple is as calloused as the bottom of a foot, imo.
category B elbow drops--
These are solid players whose elbow is still at the time of contact. The stroke is a simple pendulum stroke until after the cueball is gone. The impetus for dropping the elbow in the follow through perhaps comes from the desire to have a long, exaggerated follow through, or perhaps it comes from wanting a level, horizontal follow through (instead of the tip approaching the cloth as in the pendulum stroke). These people don't necessarily need to change anything. The biggest problem they cause is for others. They embolden the category A folk--who don't recognize the difference--thus providing a disincentive for the category A folk learning good mechanics.
Category C elbow drops--
This is, for example Mike Massey. These people are capable of a good pendulum stroke and perhaps employ a pendulum stroke on most of their shots. However, on power strokes, e.g., a break shot or a power draw shot, you will see an elbow drop. These players' elbows are moving at contact because the point is to add some speed by pivoting about the shoulder. In fact focusing on the elbow drop is like focusing on the thunder instead of the lightning. The lightning here is the elbow raise on the backstroke. Then pivoting about both the shoulder and elbow on the forward stroke increases speed. Most players, imo, should never do this for, say, a draw shot. The reason is that while the speed increases a bit, the bigger effect is our precision in where we contact the cueball goes down by a more significant amount. So I would say if you can't consistently draw one and a half table lengths with a pendulum stroke, then there's no way you should be futzing with this stuff. And if you CAN consistently draw one and a half table lengths with a pendulum stroke, then...well..you're more or less good to go!
Does an extended follow-through add power to a shot?
I think this is a question of cause and effect. A follow-through strictly has no influence on the cue ball because the cue tip is in contact with the cue ball for only a very short amount of time (approximately 0.001 seconds). The only things that significantly affect the breaking power for a given cue stick are cue stick speed at impact and tip offset (distance away from a center ball hit). However, if a powerful stroke does not exhibit a big follow-through, it is either not very powerful, or effort is being made to limit the follow-through. If one tries to constrain the follow-through, one will probably not achieve maximum speed at impact. Many authors and instructors recommend trying to "accelerate through the ball" for power shots. This thinking often helps one create good power, and it results in significant follow-through.
Follow-through can also be important in achieving good action on draw shots (although, not always for the reasons people think). For more info, see my May'06 instructional article. In particular, see item "b" under "other advice" and item "5" under "stroke best practices." I think these points apply equally well to both a power break and a power draw.
All the cue ball cares about is tip contact point, cue speed, and cue elevation at the moment of impact. Follow-through is just a symptom of your stroke and has no direct affect on the action of the shot. Now, when you follow through, maybe you are doing something different with your stroke to get a different cue speed or a different tip contact point, or maybe your stroke is straighter. You might want to videotape your stroke changes and look at the chalk mark on the CB. It helps to use a ball with markings (e.g., a striped ball or a Jim Rempe ball) when checking the chalk mark. If two shots have the same cue speed and tip contact point, but have different amounts of follow through, the action of the shots should still be the same. If you are getting different action, you are not hitting the CB with the same speed, tip-contact point, or aiming line.
Why is it usually recommended to have the forearm perpendicular to the cue at CB impact?
With a non-elbow-drop stroke, and with the forearm perpendicular to the cue, the cue tip will be moving exactly straight in the cue direction. If the grip is forward, the tip will be moving down into the ball; and if the grip is back, the tip will be moving up at impact. This might help people be more accurate and consistent with tip positing on the CB at impact. Also, there is a natural tendancy to reach a constant maximum cue speed when the forearm is vertical. This can make it easier to control your shot speed, because the speed of the cue won't be changing much just before contact. For more info, see:
HSV B.40 - stroke speed and acceleration analysis, with Bob Jewett
What is SPF or SPFF?
SPF = set, pause, finish
SPFF = set, pause, finish, freeze
from Scott_Lee:
The "set" position occurs at the CB, after your warmup cycle is finished. It's the last conscious thought about, "Well? Are you ready or not?" With the tip at the CB, the "set" position is used to verify earlier decisions on angle, speed and spin. If it is a go, there are no more warmups, and the final backswing begins. The "pause" happens as we come to the end of the natural backward motion of the cue, so we can make a smooth transition to the forward swing. All strokes start from zero, and accelerate to whatever speed you're hitting the shot with. The "finish" is exactly how you described it. The grip hand ends up in the armpit area, close to the chest; and the tip is on or close to the cloth, some distance past where the CB was sitting. The "freeze" is an opportunity for self-evaluation, that happens after the stroke is over, and you have remained motionless, except for your forearm. The freeze allows you to check components of your stroke, including the grip finish, tip finish, and speed control.
When do muscle transitions occur during the stroke?
from Spiderman:
if the real reason for a "pause" is to allow the "backswing" muscles to stop working before the "forward swing" muscles take over, then there is absolutely no need for a pause in MOTION, only a pause in acceleration.
When the "backswing" muscles relax, the stick is still moving backwards. There can be a finite period of relaxation before the "forward swing" muscles contract and apply force. AT THIS POINT, AND FOR A FINITE TIME AFTERWARD, THE STICK IS STILL MOVING BACKWARDS. It takes some finite time for the "forward swing" muscles to accelerate the stick to zero velocity. There will then be no finite time at zero velocity because the acceleration is continuous, so the stick progresses smoothly (semi-sinusoidally) from backward to forward velocity.
For this example, the "pause" was in acceleration, not velocity. This relaxation of backswing muscles and subsequent resumption of opposite force occurred entirely before the backwards motion ended.
What is the definition of "pause"?
Strictly, the word "pause" does imply stopping for more than an "instant." When a player has an obvious "pause" between the end of their back-swing and the beginning of their forward-swing, I like to refer to it as a "deliberate pause" or a "distinct pause." Here, the implication is clear: the cue is held stationary (stopped) for more than an instant.
Strictly speaking, if the cue stops only for an "instant," there is no "pause." An "instant" does not involve any passage of time. A "pause" does imply a "stop" (zero speed) for a distinct amount of time. For example, when a free-swinging pendulum changes direction at is highest point, it does "stop" for an "instant," but it does not "pause." The speed gradually and smoothly changes from negative (in the backward direction) to positive (in the forward direction), through zero. The speed does not stay at zero for any amount of time. At the tiniest fraction of a second before the speed is zero, the pendulum is moving slowly in one direction (negative speed); and at the tiniest fraction of a second after the speed is zero, the pendulum is moving slowly in the other direction (positive speed). The speed is zero only for an "instant." Not even the smallest fraction of time passes during that instant.
Now, having said all of that, I don't think it really matters that much. People will interpret the word "pause" in different ways; but as long as you are clear and consistent and people know what you mean, nothing else really matters. Again, I like to use the phrase "deliberate pause" when there is a distinct "pause" in the action (i.e., the stop occurs for more than just an "instant"). For example, both Allison Fisher and Buddy Hall (and others) obviously have a "deliberate pause" before their final forward stroke. I think the phrase "pause for only an instant" is also OK when there is no "deliberate pause"; although, it is strictly not proper. When somebody rushes or jerks the transition between back and forward motion, there still is a "stop for an instant" (because the cue still changes direction and has zero speed for an instant). I would call this a "pauseless and rushed" transition.
The pause at the set position allows your eyes to focus and verify both the tip contact point on the cue ball and the target aiming line (see quiet eyes for more info). For the "pause" at the end of the backstroke, see item 4 in the stroke "best practices" document. Adding a "distinct pause" helps some people prevent themselves from rushing the final backswing and from rushing the transition to the final forward stroke. Jerking this transition can cause stroking errors.
from mikepage:
If you watch a hundred top players and also watch a hundred ball bangers, here is what I think you will notice:
set position: On average, the top players are stopped like an oak tree in the set position for a notably longer time. The bangers have variable set pauses that are often short and sometimes they don't pause at all.
final backstroke The top players--nearly all of them-- will bring the cue back slowly following the longish set pause. The bangers will bring the cue back faster.
backstroke pause Some of the top players pause; others don't. Some of the bangers pause; others don't. The differences you will note are not so much whether the players pause but rather how smooth and fluid the transition is. Part of the bangers problem with smooth transition is not really a problem with the backstroke pause/nopause. Rather it is collateral damage from the final backstroke problem. Bringing the cue back too fast encourages a jerky transition. IMO, add a backstroke pause if it floats your boat. But if you're adding it to fix a jerky transition, then you may just be enabling the real (too fast backstroke) problem.
from Stretch:
Because when there is a mechanical error in the stroke it usually happens in the transition from back stroke to forward stroke. Simply put, the end of your backstroke is the start of your forward stroke. So if the backstroke does not come back right, the forward stroke is adversely affected. A slow drawback, and slight pause eliminates this problem. Also the pause is when you re-focus on the ob's contact point. Yes "re-focus". During the practice strokes your eyes are scanning back and forth. When you are ready a back stroke and transition can for a split second distract your focus, even if you don't take your eye off the ball! A slight pause allows you to re-focus, or burn with intensity that vital little bit. It makes one simply react to the target from the trigger position without the distraction of having any moving parts going on at the same time.
from Rod:
Players with less experience get in a hurry to shoot a shot. Doing so they snatch the cue back. I have a phrase I like to use. "Finish Your Backswing".
"Gradually" bring the cue tip to the C/B and pause, let your focus go from tip placement to the O/B during this pause, "Gradually" start the cue back, (this is important because a snatch will make your backswing short) slight pause, then slowly start forward, no matter the power needed. This is the transition area. If you start forward fast, you just wasted the preparation needed to make a smooth stroke.
What you'll find, once you learn to slow down your stroke, you'll hit the cueball exactly where intended. The reason pool players never excel is they don't grasp the importance of these fundamental movements. You have to be accurate and quick movements will surely make you loose your focus.
What is a slip stroke and why is it used?
from Bob_Jewett:
Here is an article from Billiards Digest that describes several kinds of stroke including the slip stroke: http://www.sfbilliards.com/articles/2005-10.pdf
And here is one that describes some other strokes: http://www.sfbilliards.com/articles/2005-11.pdf
Why should I bother "staying down" after a shot?
from Andrew Manning:
Staying still helps for a few reasons.
1) If you're freezing at the finish of the shot, then you're certainly not jumping or moving during the final stroke, which I think everyone agrees is a bad thing to do.
2) When you freeze at the end of the shot, you can see where your cue finished. If you didn't stroke straight through the ball, this will be evident in your finish position, and you'll be able to observe it and use that feedback to improve your stroke.
3) Staying down and continuing to sight down your cue will keep a consistent frame of reference to observe the results of your shot. Your brain can record what the CB and OB do, versus what you wanted them to do, in great detail from this perspective. If you stand up before the shot is done, you have to adjust to looking at the shot from a diffferent angle, and your brain will not be able to calculate what went right/wrong nearly as effectively. Getting the best possible visual feedback is crucial, since this feedback is drawn upon heavily by your subconscious the next time you're lining up a similar shot.
There may be other benefits as well, but I think those are the most important.