Continuity mistake: When Kersey goes into the post office and his girl is waiting in the car, Fraker and his goon knock her out and shove the car down the hill. As it goes down there is a view of the back of the car and the reverse lights are on. Then as it is about to hit the other car, the lights are now off.
Factual error: During the big final battle of the movie the bad guys throw around Molotov cocktails, bottles with a rag stuffed into the top of it filled with gasoline. Problem is that the cocktails explode and shatter glass, when in reality Molotov cocktails don't explode they simply smash. And on top of this the first few cocktails that were thrown at parked cars weren't even on fire, rendering them useless.
Other mistake: Fraker's footprints are right next to each other in Kersey's bedroom. The right footprints even with the left footprints. The only way for this to be possible is if he had hopped around the room rather than walking.
Factual error: Kern unwraps the LAW and shows the cop 2 rounds which he says can be fired from the LAW. The LAW is a use and lose type weapon, you fire it once and can't re-use it. It also does not have a handle.