look out block

When an athlete with the purpose of guarding or defending another player or area, usually an offensive lineman in football or a basketball player on defense, lets the opposing player attack the quarterback/basket without any show of push-back by the player who's supposed to protect the person or thing in need of protection; also referred to as the "lookout defense."

*defensive lineman runs right by the offensive lineman*
Offensive lineman: LOOK OUT!
*quarterback is absolutely pummeled for the sack*
ANNOUNCER: "Offensive tackle, Edwards, with the look out block on that play..."