In American football, blocking is a legal move occurring when one player obstructs another player's path with his body. The purpose of blocking is to prevent defensive players tackling the ball carrier, or to protect the quarterback while attempting to pass or hand-off the ball. Offensive linemen and fullbacks tend to do the most blocking, although wide receivers are often asked to help block on running plays and halfbacks may be asked to help block on passing plays.
As a general rule blocking is a push; one is not allowed to grasp someone or do any sort of pulling, otherwise a holding penalty will be levied. Blocking is also not permitted beyond five yards from the line of scrimmage until the quarterback has handed-off the ball to a runner, or a receiver has touched the ball after it has been passed.