What squirt (cue ball deflection), swerve, and throw effects do I need to be aware of?

A complete summary of all squirt (cue ball deflection), swerve, and throw effects and rules of thumb can be found below.

As background, here are some pertinent video demonstrations from the Video Encyclopedia of Pool Shots (VEPS):

The following diagram from Jeremiah Gage (courtesy of BullseyeBilliards) nicely illustrates the numerous interactions that occur in the execution of a shot, especially when english (sidespin) is used.

shot interactions

The numbered list below is a quick summary of important squirt (cue ball deflection), swerve, and throw effects, along with links to supporting resources. Let’s start with a short glossary of definitions and an illustration of some of the terminology used in the effects list. More definitions can be found in the online glossary, and additional info and examples can be found in the linked resources.

BHE: back-hand english
CB: cue ball
CIT: cut-induced throw
FHE: front-hand english
gearing OE: the amount of outside english that results in no throw
IE: inside english
OB: object ball
OE: outside english
SIT: spin-induced throw
squerve: combination of squirt and swerve
squirt, swerve, throw illustration

Squirt (cue ball deflection), Swerve, and Throw Effects
(everything you ever wanted to know about squirt, swerve, and throw)

Squirt:

  1. Squirt increases with the amount of sidespin.
  2. Squirt does not depend on shot speed (although, squerve does; see squirt speed effects for more info).
  3. Squirt increases with the amount of shaft endmass (e.g., a low-squirt cue has less endmass and results in less squirt).
  4. Squirt is slightly less with a heavier CB and slightly more with a lighter CB (see CB weight effects).

Swerve:

  1. Swerve increases with cue elevation and the amount of sidespin.
  2. Swerve occurs with practically all sidespin shots because the cue must be elevated to clear the rails.
  3. Swerve is delayed with faster shot speed.
  4. Swerve occurs only while the CB is sliding; once rolling begins, the CB heads in a straight line.
  5. Swerve occurs earlier with sticky cloth and later on slick cloth.
  6. Swerve occurs earlier with a follow shot than with a draw shot (see “Squirt – Part VIII: squerve effects” – BD, March, 2008).
  7. Swerve angle is larger with a draw shot than with a follow shot (see “Squirt – Part VIII: squerve effects” – BD, March, 2008).
  8. Swerve angle can be predicted and visualized using the Coriolis massé-shot aiming system.

Squerve:

  1. Squerve (net effect of squirt and swerve = net CB deflection) can be zero with certain speeds and cue elevations for a given shot distance, amount of sidespin, and cue.
  2. Squerve is less for follow vs. draw shots (see squirt tip-contact-height effects).
  3. Squirt or squerve can be canceled using back-hand english (BHE) and/or front-hand english (FHE) aim-and-pivot methods.

Throw:

  1. For small cut angle shots (i.e., fuller hits), the amount of CIT does not vary with shot speed, but increases with cut angle (see throw speed effects).
  2. For larger cut angle shots (i.e., thinner hits), the amount of CIT is significantly larger for slower speed shots as compared to faster speed shots (see throw speed effects).
  3. The amount of CIT decreases some with larger cut angles, but not by much (especially for slower speed shots) (see “Throw – Part II: results” – BD, September, 2006).
  4. Maximum CIT occurs at close to a half-ball hit (30° cut angle) (see “Throw – Part II: results” – BD, September, 2006).
  5. In general, throw is larger at slower speeds, and for stun shots (see throw speed effects and throw draw/follow effects).
  6. Maximum throw, under typical conditions, is about 1 inch per foot of OB travel, or 1/2 a ball per diamond on a 9′ table, which is about 5°.
  7. Excessive throw (more than the amount expected) can occur if there is cling/skid/kick.
  8. Both follow and draw reduce throw, and they do so by the same amount (see throw draw/follow effects).
  9. Effective throw (combined effect of throw and OB swerve) can be slightly larger with follow vs. draw shots, especially at slower speeds (and with cling/skid/kick).
  10. The largest discrepancy between throw values for stun and follow/draw shots occurs close to a half-ball hit (30° cut angle) (see throw draw/follow effects).
  11. The difference between the throw of stun and follow/draw shots is not as great at larger cut angles (see throw draw/follow effects).
  12. More sidespin gives you more SIT only up to a point. Additional sidespin beyond that point actually reduces the amount of SIT (i.e., more sidespin doesn’t always give you more throw) (see throw speed effects and maximum throw).
  13. SIT is largest for a slow stun shot with about 50% of maximum sidespin (see throw speed effects and maximum throw).
  14. The amount of throw can increase significantly as a small amount of sidespin is added, especially for a stun shot (see “Throw – Part IV: spin-induced throw” – BD, November, 2006).
  15. SIT is independent of speed (i.e., the throw is the same at all speeds) for small amounts of sidespin (see throw speed effects).
  16. “Gearing” OE results in absolutely no throw. The amount of sidespin required for “gearing” increases with cut angle. At a half-ball hit, the amount of sidespin required is about 50% (see gearing outside english).
  17. At very small cut angles, IE and OE create similar amounts of throw (although, in opposite directions) (see “Throw – Part VII: CIT/SIT combo” – BD, February, 2007).
  18. For large cut angles, a small amount of OE can result in more throw than shots with no sidespin (see “Throw – Part VII: CIT/SIT combo” – BD, February, 2007).
  19. For large cut angles, IE results in less throw than shots with no sidespin (see “Throw – Part VII: CIT/SIT combo” – BD, February, 2007).
  20. IE increases throw at small cut angles, but actually reduces the amount of throw at larger cut angles (see “Throw – Part VII: CIT/SIT combo” – BD, February, 2007).
  21. OE can cause throw in either direction depending on the amount of sidespin and the cut angle (see “Throw – Part VI: inside/outside english” – BD, January, 2007).
  22. Even for large cut angle shots (thin hits), excess OE (more than the “gearing” amount) can be applied to throw the OB in the SIT direction (see gearing outside english).
  23. The amount of throw with IE can be much more consistent than with OE if the amount of sidespin varies a little. In other words, the amount of throw varies more with tip placement for OE vs. IE. This might explain why some people prefer using IE on cut shots … because they can better anticipate and adjust for the amount of throw.
  24. The least amount of throw, and the most throw consistency, occurs with fast IE shots.
  25. With a small-gap combo with a gap size close to 3/8″ (9.5mm), the 2nd ball heads very straight (i.e., the throw effect cancels the cut effect) over a fairly wide range of 1st-ball angles, regardless of ball conditions (see small-gap combos).

In support of the last two inside english (IE) items above, see the 2nd plot on page 3 of TP A.28, which corresponds to 30° cut-angle stun shots at different speeds and varying amount of both outside english (positive in the plots) and inside english (negative in the plots). In the plot, notice how consistent and small the amount of throw is for fast-speed inside-english shots over a wide range of sidespin amounts (see the left side of the green curve, which is very low and level).

The System for Aiming With Sidespin (SAWS) covers a comprehensive system to aim accurately and consistently with sidespin over a wide range of shots.

A good summary of the basic things you need to know about throw in your game can be found at the bottom of the throw tutorial page. For a more advanced approach, see AIM – A system for practicing and learning how to adjust the target line of your shot to account for throw over a wide range of shots.

Here’s a good video by CueAndMe showing a carefully-executed experiment clearly showing the effects of cut angle and spin on throw. Results of similar experiments can be found in “Throw – Part II: results” (BD, September, 2006) and in the plot from Bob Jewett’s June, 1995 BD article.

A good technical analysis and presentation of squirt effects can be found in Ron Shepard’s “Everything you Always Wanted to Know About Cue Ball Squirt, but Were Afraid to Ask.” Here’s a good summary of squirt effects from that document.

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