In the beginning when Adonis is typing his letter of resignation he is wearing a black tie. When he turns his resignation into his boss his tie is blue. When he goes home and Mary Anne asks him how his new job is he is wearing the black tie again.
When Rocky is in the basement of the restaurant talking to Creed about the fight, Rocky's sweatshirt zipper goes up, then comes down, then goes up again.
Towards the end of the movie, after Adonis shows up at Bianca's apartment door, the top dead bolt is already in the unlocked position (north to south). Adonis and Bianca continue to dialogue and the dead bolt remains in the same position. Yet just before Bianca finally lets Adonis in, the dead bolt is suddenly in the locked position (east to west) and Bianca ends up unlocking it (north to south) to let him in.
When Adonis tries on his father's shorts, there is a stain on the mirror. Later on, the stain mysteriously disappears without anyone cleaning it.
The fight between Creed and Conlan is set at Goodison Park, England. The commentator states "100,000 fans are on their feet." Goodison Park only has a seating capacity of around 39,500.
During the final fight it's dark at Goodison Park. Mary Anne Creed is watching from her home in LA, 8 hours behind in time. It should not be dark in LA at this time.
In the scenes set in 1998, the juvenile hall has signs using the typeface Calibri, which was not released to the public until 2007.
After leaving the dressing room to enter the arena at Goodison Park, Merseyside, England, an American exit sign with red text can be seen above the door. UK exit signs are green with a pictorial of a man and a door. This was clearly not shot it the UK.
When Adonis is at the Delphi gym, which is supposed to be in Los Angeles, you can see a Pathmark behind Adonis on the other side of the street. Pathmark was a supermarket chain exclusive to the northeast.
Before the final fight there is a scene which apparently takes place in the dressing rooms of Goodison Park, Merseyside, UK. However, an American 2-pin plug socket can be seen on one of the walls.