You've already read a little bit about how the cue ball can stop in its tracks after hitting an object ball. This is caused by the transfer of energy (or force) from the cue ball to the object ball and your steady stroke. Isn't it amazing that you can actually control this effect with just a little knowledge and a lot of expertise? You'd think that hitting one ball into another would simply mean that the balls move forward in any old direction, but physics tells us otherwise, and your level of skill really can put the science into action.
It's in the Timing
Well, all that aside, the stop shot is often a draw shot with the twist of timing. To make the cue ball stop, you need to time when the cue ball makes contact with the object ball. You want the contact to happen while the cue ball is still in the sliding phase versus the spinning phase (rolling top over bottom). You can hit the cue ball with a fairly strong stroke, and since there is no spin upon contact, the cue ball will stop rather than move forward (follow shot) or back to you (draw shot).
When to Use a Stop Shot
At first glance, there are a couple of reasons you'd want to use the stop shot, but when you're playing, you may find several other reasons. The first general reason is if you need the cue ball to stop in order to set up the position for your next shot. Another reason is to avoid scratching. It allows you to pocket an object ball without sending the cue ball following into the pocket right after it.
The cue ball will always rest at the point of contact on a properly executed stop shot that is straight in line with the pocket. So the way to estimate where the cue ball will stop is to simply look at the spot upon which the object ball rests, and imagine one ball width behind it, before you pocketed it — that is … once you've perfected the shot, of course.
Angled Stun Shots
When you are executing a “stop” shot on a shot with a cut angle, you can expect the cue ball to slide to the side before coming to a stop. So, when there is an angle involved, the shot is no longer called a stop shot. It's called a “stun shot.” In fact, all shots where the cue ball is sliding (as opposed to rolling) on impact with the object ball are called stun shots. If the shot is straight in line with the pocket, the cue ball will stop (which makes it a stop shot). If it's not a straight-in shot, the cue ball will slide along a tangent line that forms a 90-degree angle with the object ball's line to the pocket.
If you have a very slight angle, you may be able to avoid the cue ball sliding to the side a little by striking the cue ball as low as you can with a slow and steady stroke. This sounds like a draw shot, but if you hit it just right, by the time the cue ball contacts the object ball the backspin will have stopped, the cue ball will hit the object ball with enough force to pocket it, and the cue ball will drift only slightly to the side.