Character mistake: When Howard's men bail the guy out who was with Bobby Saint at the arms deal, they are beating him up in Saint's club. Howard Saint (John Travolta) shoots the man responsible for not watching his son. The man fall down to his knees and then says the name John instead of Howard.
Suggested correction: John is the name of Howard's other son, who is also in the room. Bobby told the man to stay behind, and John was there when it happened, so he was asking John to vouch for him to Howard. This scene actually appears in the extended cut of the film.
Continuity mistake: Toward the end if the movie when Castle goes to Saint's compound to exact his final revenge, the first guard he kills is with a bow and arrow. Castle shoots him in the back but when the guard falls forward he reveals Castle on a perch directly in front facing him.
Suggested correction: He doesn't shoot him in the back. He shoots him in the front and the arrow penetrates through. If you slow it down, you can see the arrowhead pointing out of his back.