In American football, a trap play, or trap run, is a run consisting of a defender on the line of scrimmage (either a defensive tackle or defensive end) getting trap blocked by an offensive lineman or back from the opposite (other side of the center) side of the ball. The play is known as a "trap" because the strong side offensive lineman will "block down" on a linebacker, seemingly leaving a defensive lineman unblocked.
In American football, a trap play involves a defender at the line of scrimmage (either a defensive tackle or end) being blocked by an offensive lineman from the opposite side. This is called a "trap" because the strong-side blocker will "block down" on a linebacker, leaving another defender unblocked.