Continuity mistake: When Samuel Jackson is about to be shot by the two corrupt cops, the Vanessa Williams character comes up from behind and shoots the black one in the head and he falls down. Then, they show her talking, and the same black man's arm and partial shoulder are in the shot.
Factual error: In the scene where Shaft has chased the guy running from the drug bust and caught him in the hall with an empty gun you can plainly see the slide is locked back on the bad guy's pistol (indicating an empty magazine). When Shaft steps out to arrest him (before the bad guy jumps out of the window into the other building) you can clearly hear the 2 clicks of a firearm hammer falling on an empty chamber. With the slide locked back, the hammer is locked back also...it would never make any clicks.