The 30 degree rule, like the 90 degree rule I explained earlier, will let you know the path of the cue ball.
When the cue ball hits half of the object ball and is given a running english, the cue ball is deflected approximately 30 degrees from the target line.
The cue ball trajectory is deflected approximately 30 degrees in each of these cases:
first we know that hitting half the target ball we are at 30 degrees, and we are at the limit of the margin of error when we hit the target ball at ¼ (one quarter ball) which is a large cut angle and when we hit the target ball at ¾ (three quarter ball), it is a small cut angle.
I’m going to show you a simple way of how to know the cue ball trajectory.
Here we have a shot where the 2-ball goes into the corner pocket.
The first thing we have to do is to find the line of sight.
Once we see it we make the peace sign with our fingers (index finger and middle finger), and put the middle finger on top of this line, where the ghost ball makes contact with the 2-ball to pocket it.
The index finger will be approximately 30 degrees from this line.
Now another example using the peace sign to find the cue ball trajectory.
In this example the player has to hit his first ball, the 1-ball, and it has to end up bouncing off the side rail to be in perfect position for the 2-ball.
First you must visualize the line of sight that crosses the 1-ball into the corner pocket.
Then we make the peace sign by putting one finger on the line of sight and the other finger where the cue ball is going to make the trajectory.
When making the peace sign, remember that the middle finger must be on the line of sight of the ghost ball.
When approaching a shot the first thing you need to do is to find the cue ball trajectory, determine how to use this information to get your position for the next ball.
A good exercise to help you develop where you want the cue ball to go is to set the cue ball at an angle to each object ball and try to predict where it will go after you hit it.
It is a very good idea to put a piece of paper on the table where you think the cue ball will go, hit it and then see where it goes, so you will develop and feel more confident when you are in a game.
This is why it is important to know this rule and the 90 degree rule, now you will master a big part of your game, knowing where to leave the cue ball for the next ball.