During a match in which he defends his World Light Heavyweight title, Billy sustains an injury to his left eye which is shown to be bloodshot. After the fight, Billy speaks at a press conference but the eye is no longer bloodshot. It is bloodshot again in the next scene.
The referee mandated a 1-point reduction for Hope's opponent in the last fight. None of the final scorecards reflected a 1 point reduction although the 115-114 scorecard seemed to reflect a tie of 6 rounds each with a point added to Hope to make it 115 to 114.
During Miguel "Magic" Escobar's ring entrance Roy Jones Jr. mentions that Miguel is a hard punching Colombian just like his compatriots Sergio Martinez and Carlos Monzon. Sergio Martinez and Carlos Monzon are two very well known Argentine boxers.
The bullet that killed Maureen Hope could easily be traced back to the shooter's gun. Assuming that the bullet exited Maureen Hope's body, the bullet could have also been easily found within the room. Hence, there should not have been an unsolved murder.
After the fight, in the bedroom scene with his wife, the Bose SoundTouch 20 which is playing in the bedside is flashing orange which means it is not connected to any wi fi- so no music could be played at all even though music can be heard during this scene.
The bell rings when the referee is counting 9 and Miguel is saved from a KO. In reality, once the referee starts the 10 count, the bell cannot save you (WBF rule #4.6). But Escobar was already up before the ten count. The 'Saved by the bell' said by the commentator is merely an opinion that if the bell wasn't rung Escobar couldn't have survived another hit from Billy.
In the very beginning of the movie when Billy is getting his hands wrapped as Eli is taping his right glove, at 02:43, you can see part of the H in his fighter tattoo has been rubbed off from when his arm was resting on the chair while they wrapped his hands.
In some of the fight scenes, the ringside cameramen are seen shooting with an Arri Alexa camera. This camera would probably never be used to cover sports events. It was the actual film crew that you see in the shot.
In the Hospital scene after Billy's crash, He says "Rach" several times. Obviously referring to Rachel McAdams and not her character "Maureen".
Jimmy Lennon Jr. acts as the ring announcer for the HBO boxing broadcasts in the movie. However, in real life, Jimmy Lennon Jr. is the announcer for Showtime, and Michael Buffer is the announcer for HBO.