Continuity mistake: When Mickey is watching Apollo Creed on TV, he has one sock on. When he stands up in rage, he has both socks on.
Factual error: Even though the story is supposed to take place in late 1976-ish, the Trans Am that Rocky drives is a 1979 model.
Continuity mistake: During the final part of the "gonna fly now" scene, the number of kids around Rocky is inconsistent between shots as of when he jumps over a bench and when he is walking up the steps.
Continuity mistake: When Rocky sees his baby boy, he keeps swapping from head covered / uncovered and messy / brushed hair between shots.
Factual error: Rocky buys and drives a Trans Am. Later, we find out that he can't read after his commercial goes horribly wrong. He couldn't have a driver's license because he would need to pass the written test first. You can't take the test if you can't read the questions or the driver's manual for that matter.
Suggested correction: It's not that he can't read at all, he just reads slow and has some trouble. It may or may not be enough to hamper him from taking the test. But is it ever established that he has a driver's license? He wouldn't be the first person in Philadelphia to drive without a license.
When you can't tell the difference between simple words like rat and cat, there's a pretty good chance you can't pass a written driver's test, which is why I said he "couldn't" have a license.
Revealing mistake: In the fight against Apollo, Rocky's last punch of the second round conspicuously misses by a mile, but Apollo nonetheless acts like he has been punched, and there is a punch sound effect as well.