38 minutes into the film, Gloria Dickson's "Peggy" calls John Garfield's character "Johnnie" when he in fact is still under the guise and alias persona of "Jack Dorney." She could not know this since he has not told anyone at that point of the film. Later at 1:14:00, Smith (Gaspar Rutchek's second opponent) also calls Jack "Johnnie." Even Jack's own corner man, at 1:15:58, calls Jack "Johnnie."
When Johnny tells his manager to "Give me another drink," the manager is on Johnny's left (screen right). The next shot shows Johnny pouring the drink with his manager now on his right (screen left).
When "Jack Dorney" and some of the kids were trapped in the water tank, they swam to the bottom of the tank to lift a drain cap to let out the water so they wouldn't drown. Of course, the pressure of 10 feet of water in the tank would have exerted 500-600 pounds per square foot on that drain cap, making it much more difficult if not impossible for them to lift it.
Detective Phalen is sent by his captain halfway across the country to track down boxer Johnnie Bradfield all by himself. Then as now, members of the NYPD were/are not permitted to leave the state of New York without being accompanied, for safety reasons, by at least one other officer.
In the diner scene when Johnny drops the $50 note, one of the other diners (Bill) claims the money saying "That's not your money, That's my money." An actor in the background can be seen mouthing Bill's lines at the same time as Bill utters them.
At beginning of the film, Johnny fights in the ring in front of a packed house. In at least three separate scenes, after about twelve rows of spectators, one can see a fake "painted crowd" used to create the appearance of a house filled to capacity. The "crowd" is completely stationary, unlike the "real" crowd which is always moving, twisting, and yelling.
During the accident scene, flames can be seen before the car hits the tree and a spectacular fireball happens immediately after impact.
At 35:33, Angel punches Tommy's sternum. Tommy drops covering his navel and crotch.
In the water tank, the boys splash around, churning the water in their struggle for survival. The camera cuts to the depth gauge but the water on the surface is now barely moving.
The water tank has to have a built-in ladder on both the outside and inside for both maintenance and safety.
Even burnt, Johnnie's manager would not be mistaken for Johnnie. The manager is bigger and older than Johnnie. The detectives know that Johnnie is left-handed, and the chief could not be incompetent enough to believe Johnnie would wear his watch on his left wrist. The manager's "disappearance" would be an obvious clue as well.