In baseball, a sacrifice bunt (also called a sacrifice hit) is a batter's act of deliberately bunting the ball, before there are two outs, in a manner that allows a runner on base to advance to another base. The batter is almost always sacrificed (and to a certain degree that is the intent of the batter) but sometimes reaches base due to an error or fielder's choice. Sometimes the batter may safely reach base by simply outrunning the throw to first; this is not scored as a sacrifice bunt but rather a single.
The most opportune situations for sacrifice bunts occur when a runner is on first base, or runners are on both first and second base. The runners try to advance as soon as they see the ball bunted. A properly executed sacrifice bunt in this scenario would put the ball up the first base line with a runner on first, or down the third base line with runners at first and second. This avoids a double play and results in the runner(s) advancing to second (and third) base, "in scoring position".
A successful sacrifice bunt does not count as an at bat, does not impact a player's batting average, and counts as a plate appearance. However, unlike a sacrifice fly, a sacrifice bunt does not count against a player in determining on-base percentage. If the official scorer believes that the batter was attempting to bunt for a base hit, and not solely to advance the runners, the batter is charged an at bat and is not credited with a sacrifice bunt.
In leagues without a designated hitter, sacrifice bunts are most commonly attempted by pitchers, who are typically not productive hitters. Managers consider that if a pitcher's at bat will probably result in an out, they might as well go out in a way most likely to advance the runners. Some leadoff hitters also bunt frequently in similar situations and may be credited with a sacrifice, but as they are often highly skilled bunters and faster runners, they are often trying to get on base as well as advance runners.
A sacrifice bunt attempted while a runner is on third is called a squeeze play. A sacrifice bunt attempted while a runner on third is attempting to steal home is called a suicide squeeze.
Although a sacrifice bunt is not the same as a sacrifice fly, both fell under the same statistical category until 1954.
In scoring, a sacrifice bunt may be denoted by SH, S, or occasionally, SAC.
Notable players with 300 or more sacrifice bunts
The following players have accumulated 300 or more sacrifice bunts in their playing careers:
- 512: Eddie Collins (2B) (major league record)
- 392: Jake Daubert (1B)
- 383: John "Stuffy" McInnis (1B)
- 366: "Wee" Willie Keeler (OF)
- 337: Owen "Donie" Bush (SS)
- 334: Ray Chapman (SS)
- 323: Bill Wambsganss (2B)
- 314: Roger Peckinpaugh (SS)
- 311: Larry Gardner (3B)
- 309: Tris Speaker (OF)
- 300: Walter "Rabbit" Maranville (SS)
- Active MLB leaders (as of May 26, 2014)
- 167: Juan Pierre (OF)
- 105: Javier Vazquez (P)
- 92: Derek Jeter (SS)
- 86: Placido Polanco (3B)
- 85: Ryan Dempster (P)
- 533: Masahiro Kawai (SS) (world record)
Since the beginning of the live-ball era (1920), the career leader in sacrifice bunts is Joe Sewell with 275. He was first called up by the Cleveland Indians late in the 1920 season shortly after the death of Indians star shortstop Ray Chapman after being hit in the head by a pitch, the event which is generally regarded as the start of the live-ball era.
Though touted as good strategy by traditionalists, the sacrifice bunt has received significant criticism by modern sabermetrics. The argument here is, simply, that the value of moving a runner to another base is offset by the team sacrificing one of its limited and valuable 27 outs. An out-conceded is an out-wasted, in other words.
The following stats illustrate the argument. From 1993-2010, if a team had a runner on first base with no outs, on average it would score .941 runs from that point until the end of the inning. If a team had a runner on second base with one out, however, the average was .721 runs from that point forward. Thus, if a batter walks to lead off an inning and his team bats, that team will, on average, score almost one run in the inning. On the other hand, that team decreases its run expectancy by 23 percent if it successfully bunts and moves the runner to second with one out.  
Compounding affairs are the many difficulties, complexities, and risks involved with the actual bunting process. The runner or runners on base must have speed, or the defense may get an easy force out. A manager could feasibly pinch-run, but thenceforth his bench becomes less. The player at the plate must also lay down a quality bunt. That is, the player must lay down a bunt that does not pop up, go foul, or go straight to a fielder. Even if all goes well, if the sacrifice bunt is successful, the team must, still, get a hit to score the runner, and they now have 2 outs remaining instead of three.  
- "MLB.com Statistics".
- Tango, Tom M., Mitchel G. Lichtman, and Andrew E. Dolphin. The Book: Playing the Percentages in Baseball. Washington, D.C.: Potomac, 2007. Print.