All About Throw
Throw, that misunderstood phenomenon that makes pool balls wobble off line and ruins shots. Some players say it doesn't exist. If you don't believe it does, do this simple test, #5 on this linked About.com page.
Collision Induced Throw (CIT) is different than the throw brought on by english, aka Spin Induced Throw (SIT). What is the big difference between fast and slow strokes on that test page #5 above?
Here's another trick I like to prove throw. I press two balls together along the cushion along the long rail near a corner pocket. Then I have a student hit the first ball any speed or spin they want to sink the combo eight or nine feet away in the far corner. They miss every time they try, I make it each time. The difference?
The secret, which I reveal for a few laughs after the demonstration, is to subtly wet my fingers and then ensure where the two balls touch for the combo is wet also. The added moisture helps the balls "cling" together just long enough to make the combo every time. Moisture can increase throw just as dirt and chalk on the balls' surface most surely will.
Facts About Throw:
Unclean balls grab together and change release angles at impact.
In general, throw is larger at slower speeds, and for stun shots. For larger cut angles, (thin hits) the amount of Collision Induced Throw is larger for slow shots. The amount of CIT decreases with thicker hits but not by much (again, especially for slower speed shots).
Maximum CIT occurs at close to a half-ball hit.
A handy stroke comes when throwing balls intentionally. A lot of players know they can hit a near full cut shot and "hold" the cue ball using a bit of english. A less well known play comes cutting balls along the long rail into a corner pocket with a dash of topspin and outside english (right english when cutting to the player's left and vice versa) to have the cue ball pop off the cushion and head back toward the shooter for shape on another ball to the same pocket.
Both follow and draw reduce throw by the same amount when taken the same distance up or down from center ball. The biggest differences are noticeable near that half-ball hit and almost negligible at larger cut angles.
Added english provides Spin Induced Throw to some extent and at some point counteracts/reduces the amount of SIT. SIT is greatest for a slow stun taken with about 50% of maximum english.
"Gearing" outside english results in zero throw with the amount needed increasing with cut angle. 50% is again a handy reference as it gears a half-ball cut angle.
Faster shots reduce throw but can create more squirt with the cue ball and make life very difficult. It's almost always better for the pool shooter to learn to shoot gently and let the balls take throw and their natural paths to each pocket.
You may actually use right english and make a cue ball both deflect to your left and then swerve/curve further to your left by shooting with a very low hand bridge and stroking at an upward angle (beyond level)! This prevents the cue ball from working back toward your right.
I teach throw in lay terms as "balls clinging together before release." This is not physical reality. Impact time is nearly the same, throw or not, and the changed release angle is also immediately without a drag effect, but this idea of cling then release will help the player understand the direction of throw on any object ball.
Don't confuse throw with cue ball curve or "swerve". If your cue is hoisted high in the air with english you'll get a semi-massé or massé effect. Be near level instead and the roll is straighter and deflection is minimized with momentum mostly forward and not sideways. For fun and education, make your cue very level and shoot a striped ball to a corner pocket at different speeds with lots of english. See how the ball goes nearly straight to score the pocket?
Don't mistake throw for "difflection". All shafts with pro tapers, Predators or not, have some amount that they deflect, making a cue ball struck on its left side push off to the right and vice versa. "Squirt", on the other hand, makes the cue ball jump even when using a level cue stick for a fast-moving follow stroke.
Combination shots: Second or third balls in combos receive very little spin or throw from transferred momentum. "Fuhgeddaboudit."