In American football and Canadian football, a quarterback sack occurs when the quarterback is tackled behind the line of scrimmage before he can throw a forward pass. This often occurs if the opposing team's defensive line or linebackers 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 receiver who can catch the ball, allowing the defense a longer opportunity to tackle the quarterback.

In the NFL, yards lost on the play are added as negative yardage to the team's passing totals; the quarterback's individual passing total remains unchanged. Before that change in records-keeping was made, the tackling of a player behind the line of scrimmage resulted in a loss from that player's rushing (running) statistics, even if it was fairly obvious a pass play was intended. NCAA college football continues to subtract sack yardage from individual rushing totals.

To be considered a sack the quarterback must intend to throw a forward pass. If the play is designed for the quarterback to rush (run) the ball, any loss is subtracted from the quarterback's rushing total. If the quarterback's intent is not obvious statisticians use certain criteria, such as the offensive line blocking scheme, to decide. Other unique situations where a loss reduces a quarterback's rushing total (not a sack) are "kneel downs" (used to run time off the game clock), and aborted plays, such as a fumbled snap that the quarterback falls on to maintain possession.

A player will receive credit for half of a sack when multiple players contribute to the sacking of a quarterback.

The term "sack" was not widely used before ca. 1970; previously one would simply refer to a player's being tackled behind the line (of scrimmage), in so many words. The NFL only began to keep track of sacks in 1982.^*

"Quarterback sack" was first invented by hall of fame defensive end Deacon Jones He felt that a sack devastated the offense in the same way that a city was devastated when it was sacked.[http://www.profootballhof.com/history/release.jsp?release_id=774

NFL all-time quarterback sack leaders

1. Bruce Smith - 200
2. Reggie White - 198
3. Kevin Greene - 160
4. Chris Doleman - 150½
5. Richard Dent - 137½
6. John Randle - 137½
7. Leslie O'Neal - 132½
8. Lawrence Taylor - 132½
9. Michael Strahan - 129½
10. Rickey Jackson - 128
11. Derrick Thomas - 126½
12. Clyde Simmons - 121½
13. Simeon Rice - 119
14. Sean Jones - 113
15. Greg Townsend - 109½
16. Pat Swilling - 107½
17. Trace Armstrong - 106
18. Neil Smith - 104½
19. Jim Jeffcoat - 102½
20. William Fuller - 100½
21. Charles Haley - 100½
22. Andre Tippett - 100

Deacon Jones has said that he amassed 180½ sacks, although this is unofficial, as Jones' football career ended before the NFL tracked sacks as an official statistic. In 1967,Deacon Jones amassed 26 sacks in 14 games. It should also be noted that sacks did not become official statistics in the NFL until 1982.

Michael Strahan currently holds the record for most sacks in a single season with 22.5.

List is as of November 26, 2005. Bold denotes active players.

References

1. NFL Sack Records
2. Deacon Jones from The Pro Football Hall of Fame
3. Sack Story An article describing the controversy over the sack record

American football terminology | Canadian football terminology