Continuity mistake: When the sniper shoots at John and then he pretends to fall dead, you can see something stuck to the bottom of his shoe, but when he gets up there is nothing there.
Continuity mistake: When Denzel's son is running to 2nd base and collapses, they turn him over and there is dirt on his nose and forehead. In the next shot there is no dirt.
Continuity mistake: When John Q. gets stabbed by the young dude, you see a blood stain in his shirt. Later in the film when the sniper shoots him there is no blood stain, even though he is wearing the same shirt.