Title: List of Major League Baseball single-inning runs batted in leaders
Content:  The Major League Baseball (MLB) leaders in runs batted in (RBI) in one inning are topped by record holder Fernando Tatís, then with the St. Louis Cardinals, who set the MLB record with eight RBI in a 1999 game in which he hit two grand slams in the third inning of a game against the Los Angeles Dodgers. Alex Rodriguez set the American League mark, with seven RBI in the sixth inning of the New York Yankees' final game of the 2009 season, played against the Tampa Bay Rays. Under Major League Baseball rule 10.04, a batter is credited with a Run Batted In 
Title: List of Major League Baseball single-inning runs batted in leaders
Content:  most circumstances where the batter's action at bat causes one or more runs to score, as set forth in this Rule 10.04 As the most RBI that can be scored in a single at bat is four (with a grand slam, in which a home run is hit with the bases loaded), scoring five or more RBI in a single inning requires at least two at bats with runs batted in during each at bat in that one inning, all of which combines to make this an extremely rare occurrence. Since 1900, there have been 22 different players who have hit six or more 
Title: Run (baseball)
Content:  National League in 1892) on June 29, 1897. The modern-day record of 30 was set on August 22, 2007, by the Texas Rangers against the Baltimore Orioles. The National League record was set by the Atlanta Braves with 29 runs against the Miami Marlins on September 9, 2020. The highest combined score in a game is 49 runs on August 25, 1922, when the Chicago Cubs defeated the Philadelphia Phillies 26–23. The record for most runs scored by a team in a single inning is 18, set by the Chicago White Stockings (now the Chicago Cubs) against the Detroit Wolverines on September 6, 1883. The modern-day record is 17, achieved by the Boston Red Sox against the Detroit Tigers on June 18, 1953.
Title: Run (baseball)
Content:  15–September 3, 2000). The record for most runs scored by a player in a single game is 7, set by Guy Hecker of the American Association's Louisville Colonels on August 15, 1886. The modern-day record of 6 is shared by fourteen players (eight of whom attained it before 1900). Of the six modern-day players to score 6 runs in a game, the first to perform the feat was Mel Ott of the New York Giants on August 4, 1934 (he repeated the accomplishment ten years later, making him the only player ever to do it twice); the most recent was Shawn Green, then of the Los Angeles Dodgers, on May 23, 2002.
Title: Run (baseball)
Content:  The career record for most runs scored by a major-league player is 2,295, held by Rickey Henderson (1979–2003). The season record for most runs scored is 198, set by Billy Hamilton of the Philadelphia Phillies in 1894. The so-called modern-day record (1900 and after) is 177, achieved by Babe Ruth of the New York Yankees in 1921. The record for most seasons leading one of the major leagues in runs scored is 8, held by Babe Ruth (American League: 1919–21, 1923, 1924, 1926–28). The record for most consecutive games with at least one run scored is 18, shared by the Yankees' Red Rolfe (August 9–August 25, 1939) and the Cleveland Indians' Kenny Lofton 
Title: List of Major League Baseball single-inning runs batted in leaders
Content:  23 players have knocked in six or more RBI in a single inning in MLB play since 1900. Though the current official designation of a Run Batted In was not officially set until 1920, the six RBI knocked in by Fred Merkle for the Giants in 1911 have been counted retrospectively using the modern definition of the statistic.
Title: List of Major League Baseball single-inning runs batted in leaders
Content:  by a score of 15&ndash;4. In the second game, Tom McBride of the Red Sox came up twice in the fourth inning, clearing the bases in both at bats with a double and then a triple, yielding six runs to tie the record. As part of a 12-run sixth inning, the Philadelphia Athletics scored a 16&ndash;5 win over the Washington Senators in a game played at Griffith Stadium. Joe Astroth went 3 for 5 in the game and tied the major league record for one inning, hitting a grand slam home run and a single to knock in another two runs.
Title: List of Major League Baseball single-game runs batted in leaders
Content:  In baseball, a run batted in (RBI) is awarded to a batter for each runner who scores as a result of the batter's action, including a hit, fielder's choice, sacrifice fly, sacrifice bunt, catcher's interference, or a walk or hit by pitch with the bases loaded. A batter is also awarded an RBI for scoring himself upon hitting a home run. Sixteen players have batted in at least 10 runs in a single Major League Baseball (MLB) game to date, the most recent being Mark Reynolds of the Washington Nationals on July 6, 2018. No player has accomplished the feat more than once in his career and no player 
Title: List of Major League Baseball single-inning runs batted in leaders
Content:  in a single inning. In 1911, Fred Merkle of the New York Giants became the first player in the modern era with six RBI in an inning and Bob Johnson became the first AL player to match the number when he did so in 1937. All of the teams with a player with six or more RBI in an inning have won the game, usually in a blowout, though two of the games ended up with a two-run margin of victory: The Montreal Expos defeating the Chicago Cubs 17&ndash;15 in 1985 behind Andre Dawson, and the Boston Red Sox by a score of 19&ndash;17 
Title: List of Major League Baseball single-inning runs batted in leaders
Content:  before Tatís hit a grand slam to deep left field on a 2–0 count. Three more runs scored before Tatís would again come to the plate with the bases loaded, belting his second grand slam with two outs and a full count, to give Tatís the MLB record for most RBI in an inning and becoming the only MLB player to have hit two grand slams in a single inning. Alex Rodriguez set the American League mark in a 10–2 victory by the Yankees over the Rays at Tropicana Field on the final day of the 2009 season. Rodriguez entered the game with 

Question: most runs ever scored in a mlb inning?
Answer: 18.