When Kay Lenz' character arrives at the hospital, she is wearing white boots. Then she runs into the emergency room and she is in tennis shoes. In the next shot, she's back in white boots.
In the opening garage scene the BMW was initially in a marked parking spot but was later shown in another location when the thugs bashed the windows and pulled the woman from the car.
When Frank Bauggs car is outside the apartment block, it is positioned underneath the building adjacent to the reception. It is therefore impossible for Bauggs body to hit the car by falling out of the apartment block window.
In the opening titles as the woman walks towards her car she walks past the same ramp twice. This can be confirmed by noting the parking space numbers 26-28 also appearing twice.
The story takes place in Los Angeles, California. Yet there are some scenes with police vehicles with their emergency lights on and not displaying a steady red light in front. According to the California vehicle code, all law enforcement and emergency vehicles are required to have at least one steady red light on facing forward whenever the emergency lights are on. The police motorcycle and only one police car in the movie are shown with a steady red light while others aren't.
In the morgue scene, when the body of an eighteen-year-old male is uncovered, the "corpse's" eyes visibly move.
[46:01]In the restaurant explosion, it's obvious two dummies are blown up.
During the climax of the film (the underground parking lot scene), the car driven by one of White's henchmen comes to a complete stop briefly before it explodes.
When she is in the morgue viewing the drug victims the doctor pulls the sheet away from the face of the kid who committed the robbery (bullet hole in head) and he looks up at them.
The window is already shattered before Frank Bauggs is knocked threw it. A similar mistake was made in Raw Deal (1986) & Remo Williams: The Adventure Begins (1985)
[9:15]When Paul Kersey is reading his girlfriend Karen's newspaper article about battered women, the article reads, "A suggestion that public hearings on applications be limited to one every six months was taken under advisement by the commission." It must have been an article about zoning; nothing to do with battered women.
Around the 17th minute, when the drug dealer got shot on the roof and then falls down to the bumper cars power net, he got electrocuted. This would be impossible since he touched only the one electrode, and not the other, which is actually the metal floor where the cars move.
Ramp visible behind a parked car when police car flips, which disappears in the next shot.
During the final scene where John P. Ryan is blown up, you can see he is replaced with a mannequin, and there is an electrical cord running along the ground that wasn't there in the scenes beforehand. The cord is to set off the explosive charges to stimulate being shot with the LAW.
When Kersey is following the last thug during the opening montage the camera operator's shadow is visible behind Kersey (just before he pulls the shutter down).
At 15:41, several spotlights are visible during the close-up of the bumper cars. When the camera cuts to a close-up of Randy and JoJo, the lights in the background have disappeared.
According to a printout read by a policeman, Kersey lives at 8200 Wilshire Boulevard in west Los Angeles, yet when he returns home (before he is collected in White's limo) he drives into the garage of a house with "351" painted on the curb. Also, the city is listed as "West Los Angeles". West Los Angeles is not an incorporated city, it's a region of the city of Los Angeles. 8200 Wilshire Boulevard is not a house, it's an office building.
When Paul is pulling up outside Olivia's house when she's returning from hospital the boom is clearly reflected in the cars window as it passes.