Visible crew/equipment: Towards the end of the film, as Snyder hustles Lonnegan out of the room (Spoiler alert!), believing that Hooker and Gondorf have been killed, an extra in a pale grey suit with a red tie stands with his hands up. The shadow of a Sennheiser microphone shows up clear as day on his costume.
Factual error: When Hooker comes out of the diner there is a billboard advertisement to the right. It is for Ezra Brooks bourbon. Ezra Brooks brand wasn't created until 1957.
Other mistake: The reporting of the horse race used to sting Doyle Lonnegan stops as soon as the fake FBI agents raid the bookmakers. J J Singleton, who is reading the results of the race, stops when he sees the raid taking place. However, that was supposed to be a live broadcast from the racetrack itself. It should have continued. Lonnegan isn't stupid - he would pick up on something like that immediately.
Plot hole: Doyle attends Gondorff's betting shop three times, and he listens to the announcer calling three races from three different race tracks - Narragansett in Rhode Island, Belmont in New York, and Riverside Park in Missouri. He cannot possibly miss the fact that the same announcer calls all three races! J.J. Singleton, the race caller, has an instantly recognisable voice, and Doyle wouldn't be fooled for a second. Each race track would have had its own announcer.
Suggested correction: There are a lot of things Doyle is processing when he's in the shop. There's a lot happening, and he has a lot on his mind, and increasing pressure and stress each time. It's quite possible that he wouldn't notice the accent of the announcer, something he has no reason to doubt.
Rubbish. During his first two visits, he sits quietly listening to the race announcements. On his second visit, he would recognize J.J. Singleton's distinctive voice and would realize something was very wrong.
Continuity mistake: When Lt. Snyder breaks the phone booth window with his gun and points it at Hooker, Hooker's hat falls off. Yet in the next shot over Lt. Snyder's shoulder you can see that Hooker's hat is back on his head.
Factual error: When Lonnegan brings the briefcase full of money to the cage for his big bet, all of the 100s in the case are 60s federal reserve notes, which obviously did not exist in the 1920s or 30s.
Revealing mistake: After Hooker escapes the attack by Lt. Snyder in the phone booth, he runs down an alley. On a cross street in the distance, a modern sedan and large white truck drive by.
Continuity mistake: When Hooker meets Gondorff for the first time, he puts him in a shower, fully dressed. When the camera cuts to a front view of Gondorff, as the shot goes back and forth between him and Hooker, Gondorff's right pant leg alternates between being soaking wet and completely dry several times.
Continuity mistake: When Lt. Snyder meets with Polk, the FBI agent, they both sit down and Snyder makes a comment about Polk's "nice office," which is really an empty factory. Polk gets offended immediately and from an over-the-shoulder shot you can see him rise from his chair. The camera switches to a shot of his face and he's calmly sitting down again, then rises up in anger. He stands up twice.
Other mistake: Why is the cashier sitting behind bars in the mock-up bookies when he just steps out of the side to go and fetch Gondorf? If anyone wanted to get at the cashiers they could just walk around the side where there is no door.
Suggested correction: It's partly psychological. Also, anyone going around the bars would be slowed down, more than simply reaching over, giving the cashier the opportunity to react.
Audio problem: When Hooker first meets Gondorff he says "he didn't tell me you were a screw-up." However, when he says 'screw-up' in some versions you can't distinctly see his lips form the letter F, meaning that he actually said another, ruder word that was covered up later.
Continuity mistake: After the scene where Doyle places the bet on Blue Note for Hooker, Hooker gets onto an elevator. After the door closes, there is a visible edit. The operator switches from barely visible to standing where half of his body is visible. (01:18:00)
Character mistake: At Duke Boudreau's bar, the potential recruits for the sting are told, "Gondorff is setting up a con on the North side". Later in the film, Agent Polk tells Lt. Snyder, "Gondorff is running a con on the South side". The actual address for the betting hall is not given, but it is just down the alley from Klein's, which does have a South side address.
Suggested correction: It's possible recruits were given the wrong information on purpose until they'd been cleared for participation. Misinformation is a good way to confuse and delay any unwanted attention.
This does not correct the posting. "Polk" tells Snyder that Gondorff is running a con on the NORTH side, which is incorrect. He has absolutely no reason to try to mislead Snyder.
Other mistake: Wrecking Crew was 3-1. Ray Walston announces he paid $6.00 to win. If he was 3-1, he would have paid $8.00.
Visible crew/equipment: When Robert Redford is being chased by Lt. Snyder, he jumps from a high place to the ground. One can easily tell it's not Redford but a stunt double.
Factual error: The Helvetica typeface, used on the 43rd Street 'L' platform is not correct for the period of the film.
Factual error: When Hooker gets caught in the phone booth by Schneider, the very last shot has Hooker running down a street with a row of cars contemporary to the period parked on the left. If you look just beyond the 'prop' cars, you can see modern cars parked.
Suggested correction: This isn't a mistake. The person "operating the radio" could easily have switched it off because of the commotion. Lonnegan would simply suppose this is what had happened. He is not going to instantly suspect someone is faking the whole thing.