Continuity mistake: When Marty chases after Biff on the borrowed 'skateboard', Marty is wearing a dark grey belt and a red/blue print shirt under his red/beige jacket. However, when Marty is hanging on to the front of Biff's car as they turn a corner (and in another shot), Marty (stunt double) is wearing a light brown belt and solid tan shirt.
Trivia: Eric Stoltz was the original Marty. After filming quite a few scenes they realised he was being a bit too dramatic for the humor desired, so they cast Michael J Fox (who they couldn't originally get because he was busy with the TV show Family Ties). But filming, tiring for Fox, was worked out by filming on weekends and nights around his TV schedule and using his double at other times.
Question: Right when Marty gets back to Doc before he goes back to 1985, he's praising his dad's actions of the night. One line that's bothered me ever since I can remember is "My dad laid out Biff. He's never stood up to Biff in his life." And then the Doc pauses for a second and gets a strange look on his face and says, "Never?" To that, Marty says, "No, why?" and the Doc shrugs it off saying, "Nevermind." What's Doc thinking? The best I can come up with is that he's wondering what effects it'll have on the future, but that's a rough guess. If anyone out there knows, I'd be happy to hear it.DenizenZERO