Usually, there are 5 offensive linemen blocking for the quarterback when he is going to attempt to throw a pass. Also, usually there are 4 defensive linemen trying to rush the quarterback to try and stop the pass play. When a 'blitz' is called by the defense, extra defensive players additionally rush the quarterback to try and stop the play. This can be as few as 1 extra person to 3 or even 4 players from the defensive side rushing to try and get the quarterback before he has a chance to pass the ball. As an additional twist, some defensive plans have what they call a 'run blitz'. This occurs mainly on a short yardage play, where as many as 9 or 10 defensive players may line up within 2 yards of the line of scrimmage to try and stop the running back from gaining the necessary yardage to convert the play into a first down. There are too many variations of 'blitzes' to name them all. The basic idea is to bring more people on defense than the offensive people can block, thus disrupting the play and stopping the offensive play. If a quarterback or running back can elude the blitzing defensive players, it can sometimes turn into a big play for the offense as there are less defenders to tackle the offensive player who gets the ball.