High Quality Content by WIKIPEDIA articles! In American football and Canadian football, a sack occurs when the quarterback is tackled or run out of bounds behind the line of scrimmage before he can throw a forward pass. This often occurs if the opposing team's defensive line, linebackers or defensive backs are able to quickly get past blocking players of the offensive team, the quarterback's protection; or if the quarterback is unable to find, in a reasonable amount of time, an available eligible receiver including running backs and tight ends who can catch the ball, allowing the defense a longer opportunity to tackle the quarterback. In the NFL, it is possible to record a sack for zero yards. The QB must pass the statistical line of scrimmage to avoid the sack.