During the last pool match, second game, Minnesota Fats has taken his jacket off, loosened his tie and unbuttoned his vest, but one subsequent shot shows him with his tie tightened and wearing a buttoned vest and jacket.
When Sarah writes words on the mirror, she writes "TWISTEd" - all capital letters except for the "d". When it is shown later, when Eddie is in the room, it is written in all lower case letters.
In the last game with Fats, Eddie starts by calling and pocketing the 1 ball and the 12 ball. Eddie is talking to Bert as he sets up his next shot, a 4 ball, which he then pockets. His next string of calls - the 5 ball, the 14 ball, and then the 4 ball again (which he had already pocketed).
When Eddie puts on his coat and calls Fats "beautiful", his coat collar is turned under. He turns around while laughing, and when he turns back to face the camera, his coat collar is out, in its proper position.
During the last match between Fats and Eddie, in the first game, Fats attempts a soft break, leaving the cue ball against the rail. In the establishing shot, the cue ball is clearly bouncing away from the rail, in the next shot, the ball is tight frozen against the rail.
Early in the movie after Eddie and Fats make some "Safe" calls, Fats calls the seven in the corner closest to him. He shoots and it does go in the corner pocket but when the cue ball is heading for the same corner pocket for a scratch, the camera quickly cuts away. The patrons in the hall applaud the shot.
After having his thumbs broken, Eddie is wearing large casts on both hands. Clothing changes that occur later would be impossible because the sleeves on the shirt and jacket that Eddie wears could not fit over the casts.
At the Parisien Restaurant, Sarah orders sherry, but the waiter brings and pours from a bottle labeled Valpolicella, that Eddie approves.
After thugs break his thumbs, Eddie wears cast on his hands that remain sparking white for weeks - an impossibility because casts are dirt magnets that quickly become dingy-looking under the best of conditions and he's seen spilling coffee on them, lives in a seedy apartment, goes outside for a picnic and so on.
In the early pool scene Fats takes two shots left-handed although he is a right-handed player. Good pool players usually play almost equally well with both hands.
Eddie is referred to as "boy" several times in the movie. Paul Newman was 36 years old when he made The Hustler, far too old to be considered a "boy".
In the scenes with Paul Newman in her apartment early in their love affair, Piper Laurie's lines as Sarah are overdubbed. You can hear an audible dead spot in the soundtrack just before and after Paul Newman's Fast Eddie responds to her lines. Clearly a post-production issue and a distracting aspect of Laurie's performance in the film.
During Findley's party, all of the musicians fingers are out of sync with the rhythms of the music. Most noticeable is the clarinetist.
When Eddie returns to Sarah's apartment after he's been beaten up, he tells Sarah that they broke his 'thumb'. Later, Eddie has both his hands in plaster and announces that they broke 'both of his thumbs'.