Position of Kate's Jeep at the beach house. Early on, we see her Jeep facing the water with the driver's side door closest to the beach house. Later, when Gaerity secures the latch on the hood, we see that the Jeep is facing away from the water and the driver's side is away from the beach house.
When the bomb truck is "blown away" Jimmy, who is in close proximity to the explosion, falls toward the explosion. This action goes against the laws of physics seeing as the explosion flipped the truck onto its roof.
When disarming the device on Anthony's head and the second device in the speaker, Bama is told he doesn't need to be there. As he gets up you can hear and see Bama drop the side cutters onto the shelf, but when he leaves you see him pass them to Jimmy.
When Forest Whitaker's character Anthony Franklin is jogging outside, he runs up a flight of stairs and stops right in front of the camera. The piece of tape marking the spot at which he is supposed to stop is clearly visible.
When Jimmy is driving his motorcycle to his house after getting off the phone to Ryan he turns the corner and sparks fly but no part of the bike touches the ground but you can see the spark stick on the back left wheel.
The final car crash scene occurs near Boston Common on the corner of Joy and Beacon Street, as the car comes out of Joy onto Beacon. While it appears that much of the footage was filmed on Joy or adjacent streets, it could not have happened the way it did in the movie. Joy Street is only about a quarter mile long, and all but the final half block (shown correctly in the movie) is uphill when going toward Boston Common. This would obviously ruin the plot line that they couldn't apply the car's brakes. The stunt sequence when Jimmy jumps to the jeep from the motorcycle was shot going down Anderson St. on the other side of Beacon Hill (northbound) where it crosses Phillips. (A lot of movie lights are visible in the open, though.)
The Guinness in McDowell's Pub has no head. A thick creamy head is a distinctive characteristic of Guinness. No "Irish" barman would serve Guinness in such a manner, nor would any true Irishman drink it. The Guinness was also served in the wrong glass.
There is a clip of a Red Sox game on the TV. When Mo Vaughn hits the homerun, the announcer says it's "over the green monster". The green monster is the name for the left field wall. Vaughn clearly hit it over the right-center field wall, nowhere near the green monster.
During Blanket's funeral, Lt. Dove is wearing a star on his shoulder and Capt. Rourke is wearing two stars. In the Boston PD, there are not 1 or 2 star ranks. A lieutenant is a single gold bar and a captain is two gold bars.
In one of the shots of the Boston Pops playing the 1812 Overture you can see very clearly Pops conductor and Star Wars composer John Williams conducting the orchestra, then when the music ends there's a different guy conducting.
Jimmy discharges his pistol in the hot-tub when Kate shows up and the slide retracts to the empty position. Later in the scene when the pistol is sitting on the edge, the slide has retracted to a ready position. When Kate leaves to prepare for the concert, the slide has retracted to the empty position again.