Fouls by Double Hits Explained

Double Hits:

When the distance between the cue ball and the object ball is less than the width of a chalk cube, if the cue stick strikes the cue ball more than once on a shot, or if the cue stick is in contact with the cue ball when or after the cue ball contacts an object ball, the shot is a foul.

Judging Double Hits: 

Special attention from the referee is required. The following guidance may apply: 

If the cue ball follows through the object ball more than 1/2 ball, it is a foul. 

If the cue ball follows the object ball at the same speed, it is obviously a double hit and a foul.

Some rules of play may require the cue ball be struck at a minimum of a 45-deg angle to the object ball to avoid a double hit. 

Even then, if the cue ball doesn’t immediately follow the tangent line to the point of contact, it is a double hit and a foul.

Frozen Balls:

If the cue ball is frozen to the object ball, it is legal to shoot toward the object ball and have the cue ball follow the object ball at the same speed. 

The referee should confirm that the balls are frozen.

Playing away from a frozen ball does not constitute having hit that ball.