Also pool shark, poolshark (US); sharp, pool sharp (British)
1. Verb: To perform some act or make some utterance with the intent to distract, irritate or intimidate the opponent so that they do not perform well, miss a shot, etc. Most league and tournament rules forbid blatant sharking, as a form of unsportsmanlike conduct, but it is very common in bar pool.
2. Noun: Another term for hustler.
3. Noun: A very good player. This usage is common among non-players who often intend it as a compliment and are not aware of its derogatory senses (above).