Revealing mistake: In one of the major battles the old Scot gets his arm chopped off right over the wrist. You can see his prosthetic arm falling out of position after the cut. (01:27:00)
Factual error: The film hints that Wallace is the father of Isabella's child (and the ancestor of all future kings and queens of England) but Isabella's baby (the future Edward III) was born in 1312, seven years after Wallace's execution in 1305.
Visible crew/equipment: At Stirling right before Wallace drops his sword and picks up an axe you can see some black duct tape on his sword. A man then swings his sword at the exact position of the duct tape. This is an obvious test take where they rehearse the scene, and was not meant to end up on screen. (01:27:00)
Factual error: The voice-over at the beginning of the film tells us that Malcolm Wallace was a commoner with his own lands and constant references are made through-out the film to William being a commoner. However this is a common historical myth. Malcolm Wallace was in fact born as a minor noble and became a knight, as was William. They were poor as noble families went but were still infinitely more privileged than the commoners of the day.
Deliberate mistake: In the funeral scene of Wallace's father and brother, the little girl picks a flower for young Wallace. Look closely when she picks the flower- its already been cut. [This was to make it easier for the little girl to pick it so not to hurt herself on the thorns.]. (00:11:20)
Visible crew/equipment: At the end of the wedding party scene, when the Scott shrugs off the English soldier who is taking his wife, you can see a spotlight covered with a blue tarp, behind his head. (00:23:55)
Visible crew/equipment: When Wallace captures the fort of the noble who killed his wife, he pushes said noble down a hill before putting him to the post and slitting his throat. If you watch when the noble is pushed, he rolls over and the cape uncovers the back of his costume. You can see blue pants that look like jeans under his costume. (00:45:40)
Factual error: Malcolm Wallace had three sons: John, William, and Malcolm. He was not killed in a minor scuffle with the English. He, in fact, fought for several years with the English in order to free John de Baliol from the tower of London. At the time, Baliol was the rightful heir to the Scottish crown, and that was actually William's reason for fighting the English. Robert the Bruce was the one who actually liberated Scotland, right?
Factual error: In the opening scene of the film a caption at the bottom of the screen tells us it is Scotland 1280 AD and the voice-over tells us the King of Scotland had died without an heir etc. But Alexander III of Scotland did not die until 1286 AD.
Revealing mistake: When Wallace rides into the village after his wife is killed, he hits the foot soldier with the mace-like weapon. When his horse is lanced, note that the lance is actually attached to the leather girdle on the horse, so, in effect, the animal is merely being pushed over.
Continuity mistake: When William comes to take Murron on a horse ride in the rain, he talks to Murron's parents. The camera cuts to Murron a couple of times, ducking under the shelter, and her hair is completely dry. But when she rushes out and jumps onto William's horse, her hair is soaked. Obviously this scene took several takes, and they didn't take the time to dry the actress's hair between each take.
Continuity mistake: During the scene in which William Wallace is being executed, the camera pans the crowd and shows the ragged peasants staring in silence. An extra, who is a young woman with light hair and a dirty face and is standing near the front of the shot, stares directly at the camera for a few seconds while all the other extras look in a different direction towards the execution. (02:44:00)