Revealing mistake: When Robin jumps off the scaffold after being saved from hanging, you can see one of the soldiers spear tips bend under his weight.
Revealing mistake: At the end, when Guy loses the sword fight with Robin Hood, his body topples over a parapet and falls to the stone floor below. In the initial shot of him falling, it's a stunt man (who apparently broke his ankle in the process, according to the dvd commentary), but the next shot of the body landing makes the use of a dummy a little too obvious: the "corpse" bounces back up several inches before settling to the floor. (01:30:00)
Revealing mistake: At the end of the fight on the log between Robin and Little John, John's quarterstaff bangs down onto the log some distance away from the foot (of Robin) it is meant to have stabbed.