Walk-off home run

In baseball, a walk-off home run is a home run that ends the game. For a home run to end the game, it must be hit in the bottom of the final inning and generate enough runs to exceed the opponent's score. Because the opponent will not have an opportunity to score any more runs, there is no need to finish the inning and the teams can walk off the field immediately. The winning runs must still round all three bases and be counted at home plate. A variant of the walk-off home run, the walk-off grand slam, occurs when a grand slam exceeds the opponent's score in the bottom of the final inning and ends the game.

History and usage of the term
Although the concept of a game-ending home run is as old as baseball, the adjective "walk-off" attained widespread use only in the late 1990s and early 2000s.

The first known usage of the word in print appeared in the San Francisco Chronicle on April 21, 1988, Section D, Page 1. Chronicle writer Lowell Cohn wrote an article headlined "What the Eck?" about Oakland reliever Dennis Eckersley's unusual way of speaking: "For a translation, I go in search of Eckersley. I also want to know why he calls short home runs 'street pieces,' and home runs that come in the last at-bat of a game 'walkoff pieces' ..." Although the term originally was coined with a negative connotation, in reference to the pitcher (who must "walk off" the field with his head hung in shame), it has come to acquire a more celebratory connotation, for the batter who circles the bases with pride and with the adulation of the home crowd.

Jim Thome holds the MLB record for most career walk-off home runs with thirteen, the first being hit on June 15, 1994 and the last (which broke the previous record of twelve) on June 23, 2012. Most notably, he hit his 500th career home run for a walk-off home run.

Other types of "walk-off" wins
Sportscasters have applied the term "walk-off hit" to any kind of hit that drives in the winning run to end the game. It is an expansion of the term to call a hit a walk-off when what ends the game is not the hit, but the defense's failure to make a play. The terms "walk-off hit by pitch", "walk-off walk" (a base on balls with the bases loaded), "walk-off wild pitch", "walk-off reach-on-error", "walk-off steal of home", "walk-off passed ball", and "walk-off balk" have been also applied, with the latter dubbed a "balk-off". The day after Eric Bruntlett executed a game-ending unassisted triple play for the Philadelphia Phillies against the New York Mets on August 23, 2009, the Philadelphia Daily News used the term "walk-off triple play" in a subheadline describing the moment, although it was not a true walk-off.

Walk-off grand slam
A grand slam is a home run hit with all three bases occupied by baserunners ("bases loaded"), thereby scoring four runs—the most possible in one play. A walk-off home run with the bases loaded is therefore known as a walk-off grand slam. Since 1916 there have been more than 250 walk-off grand slams hit during Major League Baseball's regular season. From 1903 onwards, only one walk-off grand slam has been hit in the postseason, by Nelson Cruz of the Texas Rangers in Game 2 of the 2011 ALCS.

The most recent walk-off grand slam was hit by Cal Raleigh of the Seattle Mariners on June 10, 2024 against the Chicago White Sox.

Three players have hit two walk-off grand slams in a season, Cy Williams in 1926, Jim Presley in 1986, and Steve Pearce in 2017. Pearce's first was on July 27 (an 8–4 victory over the Oakland Athletics) followed by his second on July 30 (an ultimate grand slam, for an 11–10 win over the Los Angeles Angels), becoming the first player in MLB history to hit multiple walk-off grand slams within the span of a single week.

Only five pitchers in major league history have surrendered two game-ending grand slam home runs in one season, according to the Elias Sports Bureau:
 * Satchel Paige of the St. Louis Browns, in 1952, to Sammy White of the Boston Red Sox on June 30, and to Eddie Joost of the Philadelphia Athletics on July 15.
 * Lindy McDaniel of the Chicago Cubs, in 1963, to Bob Aspromonte of the Houston Colt .45s on June 11, and to Jim Hickman of the New York Mets on August 9.
 * Lee Smith of the California Angels, in 1995, to Mark McGwire of the Oakland Athletics, on June 30, and to Albert Belle of the Cleveland Indians on July 18.
 * Francisco Rodríguez of the New York Mets, in 2009, to rookies Everth Cabrera of the San Diego Padres, on August 7, and Justin Maxwell of the Washington Nationals on September 30. Rodríguez is the only pitcher to surrender two game-winning grand slams to two rookies.
 * Bud Norris of the Los Angeles Angels, in 2017, to Edwin Encarnación of the Cleveland Indians, on July 25, and Steve Pearce of the Toronto Blue Jays on July 30. Norris surrendered both in the same week, and it was the second game-winning walk-off grand slam by Pearce in the same week.

Ultimate grand slam
A walk-off grand slam that erases a three-run deficit is also called an ultimate grand slam. There have been 32 such instances documented in major league history – all taking place during the regular season, 16 of those coming with two outs. Of the 32 home runs, only Roberto Clemente's was hit inside the park, at spacious Forbes Field on July 25, 1956. Pirates manager/third base coach Bobby Bragan instructed him to stop at third, but Clemente ran through the stop sign to score the winning run. Alan Trammell's June 21, 1988 and Chris Hoiles' May 17, 1996 grand slams occurred under the most dire situation: bases loaded, two outs, full count, bottom of the ninth inning, and down by three runs. Donaldson's and Stanton's aforementioned walk-off grand slams are each the two most recent occurrences of an ultimate grand slam.

Walk-off celebrations
Walk-off celebrations typically consist of an entire baseball team leaving the dugout to meet a player at home plate after the batter hits a walk-off home run, or at whichever base the hitter happens to reach if a traditional base hit results in a walk-off victory.

A walk-off celebration may involve hitters jumping on home plate before being encircled and caught by their teammates. During a walk-off celebration on May 29, 2010, Kendrys Morales, then a member of the Los Angeles Angels of Anaheim, broke his left leg from jumping on home plate while celebrating a walk-off grand slam off of the Seattle Mariners. As a result of this injury, team manager Mike Scioscia instituted new guidelines for his team that ensured a much tamer response to all subsequent walk-off victories.

Relevant rules
The rules of baseball provide that:
 * A batter is entitled to a home run only "when he shall have touched all bases legally." (Rule 5.05(a)(5); also 5.06(b)(4)(A))
 * A batter is out, on appeal, for failing to touch each base in order or for passing a preceding runner. In some cases, all runs that score are negated.  (Rule 5.09(b)(9), 5.09(c)(2) and 5.09(d))
 * On a game-winning hit, a batter is credited for the full number of bases only if "the batter runs out his hit." (Rule 9.06(f))
 * A game-winning home run is allowed to complete before the game ends, even if it puts the home team ahead by more than one run. (Rule 7.01(g)(3), Exception; also 9.06(g))

The first point above was problematic in the 1976 American League Championship Series between the New York Yankees and the Kansas City Royals. The Yankees and Royals entered the bottom of the ninth inning of the decisive fifth game with the score tied, 6–6; Mark Littell was the pitcher for Kansas City, and Chris Chambliss was the first batter for New York. Chambliss hit Littell's first pitch into the right field bleachers to win the game and the American League pennant for the Yankees. However, Yankees fans ran onto the field at Yankee Stadium to celebrate the victory, and prevented Chambliss from rounding the bases and touching home plate. Recognizing the impossibility of Chambliss successfully negotiating the sea of people who had been on the field, umpires later escorted Chambliss back out to home plate and watched as he touched it with his foot, thereby making the Yankees victory "official". (A comment to Rule 5.08(b) permits the umpires to award the run if fans prevent the runner from touching home plate.)

The third point above led to Robin Ventura's "Grand Slam Single" in Game 5 of the 1999 NLCS. In the bottom of the 15th inning, the New York Mets tied the score against the Atlanta Braves at 3–3. Ventura came to bat with the bases loaded, and hit a game-winning grand slam to deep right. Roger Cedeño scored from third and John Olerud appeared to score from second, but Todd Pratt, on first base when Ventura hit the home run, went to second, then turned around and hugged Ventura as the rest of the team rushed onto the field. The official ruling was that because Ventura never advanced past first base, it was not a home run but a single, and thus only Cedeño's run counted, making the official final score 4–3.

The fourth point above was not a rule prior to 1920; instead, the game ended at the moment the winning run scored. This rule affected the scoring of 40 hits, from 1884 to 1918, that would now be scored as game-winning home runs. Babe Ruth would have been credited with 715 career home runs had the modern rule been in effect in 1918; in a 10-inning game Ruth's fence-clearing, walk-off RBI hit was scored a triple because the game was deemed over when the lead baserunner reached home.

List of walk-off home runs in the postseason and All-Star Game
In the charts below, home runs that ended a postseason series are denoted by the series standing in bold. Home runs in which the winning team was trailing at the time are denoted by the final score in bold. Grand slams are denoted by the situation in bold.

Notable fictional prospective walk-off home run
Although the term itself would not be used until over 100 years later, Casey at the Bat, an 1888 poem by Ernest Thayer, features a potential walk-off home run. Although pessimistic at first, the home team's fans become more optimistic when their star, Casey, unexpectedly gets a chance to hit a walk-off three run home run. In the end they go home disappointed, however, when Casey strikes out rather than hitting the home run the fans expect.