When Johnny and Brad are playing their final game, there is a wide shot that shows Uncle Mike in the background, before he shows up.
After Johnny excuses himself from Beth's posse at the party, he asks the waiter if they "have anything in this joint besides champagne." The waiter shakes his head no, and Johnny says "Thought so." However, in the prior shot, when Johnny is explaining how he makes money, Larry can be seen holding a rocks glass containing an amber-colored liquor, presumably Scotch.
The people standing behind Johnny when he bets Chico $20,000, change twice between shots.
Danny shuts the door when he breaks into the pawn shop, but when he leaves, it is open again.
When Nick scolds Johnny for playing like a loser, the sides of Nick's cap go from being straight to folded under.
In most of the break shots, their rack is illegal. Eight Ball regulations only require three balls to be in a position in the rack: Obviously, the 8 ball in the center _and_ the two corner balls must be one solid and one stripe. That's it. However, in most (if not all of the scenes) the corner balls are of the same group.
When Johnny plays against Chico early in the film, he makes a shot with the cue ball frozen against the 8 which is on the rail near the corner pocket. This is a "push" and is not a legal shot even in a pool hall. Any shot where the cue's tip is in contact with the cue ball and the cue ball is in contact with the object ball is a push.
When Nick is talking to Johnny after Tara kicks Johnny out of the apartment, one shot of Nick is flipped. This is obvious by the New York Yankees symbol on his hat and his jacket.
The aforementioned upside-down guitar is also seen with a plastic film over the pick-guard. This plastic film is found on new guitars and usually removed before it's first played.
Danny is playing a right-hand model Fender acoustic left-handed or upside down, but the guitar hasn't been restrung for a left hand player.
In the beginning of the film, the letter from the pro tour had an 888 number to call. Later the moves states "15 years later" to bring it to the present. There were no 888 numbers 15 years ago.
When Danny is performing on stage he stops singing at the end of the song, but his voice continues.
When Johnny first meets "Uncle Mike", they discuss the chalk on Mike's pants. Johnny mentions that blue chalk is only ever found on a pool table. In actuality, the same color blue chalk is commonly used for snapping lines in construction, something that Johnny had just attempted as a profession.
As Danny explains why Chris is losing, Brad takes aim at the 6 instead of the cue ball, and the sound effects suggest he hit it.
Near the beginning of the film, after Brad refuses to play Johnny on Chico's money, Chico responds with "You know what, f*** you, Johnny," calling Brad by the wrong name.