<P> In baseball, 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 . According to The Dickson Baseball Dictionary, the term originated in the card game of contract bridge, in which a grand slam involves taking all the possible tricks . The word slam, by itself, usually is connected with a loud sound, particularly of a door being closed with excess force; thus, slamming the door on one's opponent (s), in addition to of course the bat slamming the ball into a home run . </P> <P> Roger Connor is believed to have been the first major league player to hit a grand slam, on September 10, 1881, for the Troy Trojans . Although Charlie Gould hit one for the Boston Red Stockings (now the Atlanta Braves) in the National Association (NA) on September 5, 1871, the NA is not recognized by MLB as a major league . </P> <P> Alex Rodriguez has 25 career grand slams, the most by any player in Major League Baseball history, passing Lou Gehrig's 23 on September 20, 2013 . Meanwhile, Don Mattingly set the one - season record with six grand slams in 1987--remarkably, the only grand slams of his major league career . Travis Hafner tied Mattingly's Major League record in 2006, while in 2009, Albert Pujols tied the one - season National League record of five grand slams set by Ernie Banks in 1955 . </P> <P> Several grand slams, the first being Connor's in 1881, consisted of a player hitting a walk - off grand slam for a one - run victory; some baseball observers call this an "ultimate grand slam". Steve Pearce was the most recent to do so in an 11 - 10 victory by the Toronto Blue Jays over the Los Angeles Angels of Anaheim on July 30, 2017 . Roberto Clemente is the only player to have hit a walk - off inside - the - park grand slam in a one - run victory; the Pittsburgh Pirates defeated the Chicago Cubs 9--8 on July 25, 1956 at Forbes Field, a park known for its spacious outfield . </P>

Mlb record for most grand slams in a season