This question already has an answer here:
Below is a position from a match between O'Sullivan and Hendry. Hendry has just nudged the cue ball into the pack of reds.
Obviously O'Sullivan could just do the same thing, hitting the cue ball into the pack very softly so it just barely touches one of the reds. Then both of them could just do that forever. Is there a rule that prevents this behavior?
Note that in straight pool there are specific rules to prevent this from happening, but in snooker, no such rule seems to exist.