Continuity mistake: After Marty borrows the improvised skateboard from the boy, in the first close-up of his feet his tied looped laces are extremely short, but when he climbs over Biff's moving car and then lands on the skateboard, the length of his tied looped laces is significantly longer. It shortens again thereafter.
Continuity mistake: At the clock tower, after the tree limb falls, Doc Brown grabs the loose, messy bundle of rope and instructs Marty, but in the next shot when Doc runs up the stairs, the rope is tied up in a rather tidy bundle. This rope bundle changes yet again as he rushes up and then reaches the top.
Continuity mistake: Moments before Doc and Marty witness the DeLorean's first trip through time, Doc's left hand changes its position on the radio control unit between shots. Initially he's holding a toggle switch, but after saying, "You're gonna see some serious s***," he has a grip on the unit's side instead.
Continuity mistake: At Twin Pines Mall, when Marty is recording Doc Brown, Marty is raising the video camera to record Doc Brown saying, "No, no, no, this sucker's electrical," but when this piece of film is played back in the Doc's garage in 1955 it appears as if Marty was already recording when the Doc starts speaking.
Continuity mistake: When the clock tower tolls at 10:00, Marty rushes to the DeLorean and as he drives off there are two huge cable spindles at the curb's red edge, near the cloth (lying on the street) that covered the DeLorean. In the next overhead shot, with Doc Brown on the ledge, the cable spindles are gone down below.
Continuity mistake: Inconsistent mileage progression on the DeLorean at the beginning of the movie has already been noted. However, mileage when Marty is going back to the future is also inconsistent, both in those scenes and with the beginning of the movie. As Marty is driving toward the cable, the mileage is shown as 33051. Just as Doc begins to slide down to reattach the cable, the odometer is visible again and shows 33044. These scenes were obviously filmed out of sequence, and were filmed before the beginning scenes (32994, 32064, etc) of the movie.
Continuity mistake: When the DeLorean sets off for the lightning strike, you can see it leaving tracks and spray on a wet road, later there is a close up of one of the wheels, which shows the road to be dry. Throughout this scene the road appears to alternate between wet and dry, during what is supposed to be a storm.
Continuity mistake: School Cafeteria 1955, Biff groping Lorraine Baines. Between Marty trying to convince George McFly that Lorraine fancies him and pulling Biff off Lorraine, note the dis/reappearance of the child in a blue/red t-shirt and a man in a blue shirt/tank top sat at the table behind George.
Continuity mistake: After the clock tower's ledge breaks and Doc's hanging off the edge, we see a shot from below, then of Doc looking straight up at the clock, which changes to 10:03. But look at the clock in the below shot: the minute hand ticks over behind him, then moves again in the close-up.
Continuity mistake: Just as Marty is going to be set back to 1985, the camera keeps showing shots of Marty, and the lightning poles coming closer and closer to him. Now Marty is supposed to be going 88MPH and mostly every shot just as the lightning is about to strike is basically the same distance from the lighting poles to the car.