Adam Troy Dunn (born November 9, 1979), nicknamed "Big Donkey", is an American former professional baseball left fielder and first baseman. He played 14 seasons in Major League Baseball (MLB), primarily for the Cincinnati Reds. A two-time MLB All-Star, Dunn was known for his prodigious power and his high propensity to strike out. He hit 38 or more home runs in seven straight seasons, tied with Babe Ruth for the second-longest such streak in MLB history, and was 11th all-time in at bats per home run at the time of his retirement. In addition, in 2004, he hit the fourth-longest home run in MLB history, a 535-foot blast that landed in a different state. However, he ranks third on the all-time strikeout list, with 2,379, and still holds the American League record for most strikeouts in a single season, with 222 in 2012.
Dunn's statistical profile was highly unusual for its day; he walked, struck out, or homered in nearly half his career plate appearances. Consistent with the principles of the then-emerging sabermetric movement, Dunn helped prove that a batter could significantly contribute to his team despite an unimpressive batting average. However, his defense was panned by both traditional scouting methods and modern defensive metrics. Jayson Stark called Dunn "the most unique baseball player who ever lived."
Dunn was a dual-sport athlete at New Caney High School near Houston, Texas, playing both baseball and football. Although Dunn was naturally right-handed, his father Skip taught him to bat left-handed after noticing that he hit for greater power as a lefty. Growing up, he cheered for the hometown Houston Astros. After his graduation from high school, the Cincinnati Reds drafted Dunn in the second round (50th overall) of the 1998 Major League Baseball draft.
New Caney retired Dunn's football and baseball numbers in 2015. It also named its baseball field after him.
A standout football quarterback, Dunn went 24–9 in three seasons as a starter in high school and won the district championship in his senior season.
Dunn was recruited by Notre Dame, Tennessee, and Texas A&M, but committed to the Texas Longhorns football team as part of Mack Brown's first recruiting class. He struck an agreement with the Cincinnati Reds which allowed him to play for the Longhorns during the college football season.
However, Dunn never played a snap in a competitive game. He redshirted his freshman season. Although he started the season as the No. 3 quarterback, he found himself backing up Major Applewhite after Richard Walton was injured. With Applewhite entrenched in the starting role for the foreseeable future and star recruit Chris Simms arriving on campus, Dunn was asked to move to the tight end position in spring 1999. He briefly practiced as a tight end, but ultimately left the Longhorns to concentrate on baseball. He called it "probably the hardest decision I'd ever had to make."
Dunn played four seasons in the minor leagues. Although he did not exhibit the drastically low batting averages of his major league career - he never batted lower than .281 - he showed strong plate discipline at an early age, and never posted an on-base percentage lower than .404.
The Reds offered to promote Dunn straight from A-ball to the major leagues near the end of the 1999 season (see Cup of coffee), but Dunn declined the call-up, preferring to focus on refining his swing. The Reds also invited Dunn to major league spring training, where infielder Chris Sexton gave him the nickname "Big Donkey."
Entering the 2001 season, Dunn was ranked highly by several Minor League Baseball analysts. John Sickels ranked Dunn at No. 18 in the nation, and Baseball America ranked him at No. 33. He had a banner year. He was promoted to Double-A to start the season and dominated, hitting 12 home runs and drawing 24 walks in 39 games. He was quickly promoted to Triple-A, where he continued his hot streak, hitting 20 home runs and drawing 38 walks in 55 games. He was invited to the All-Star Futures Game, where he hit a 400-foot home run. He reached the major leagues by July.
The Reds called up Dunn to the majors on July 20, 2001. He promptly set a National League rookie record for the most home runs in a month by hitting 12 in August; the record stood for 16 years, until Cody Bellinger hit 13 home runs in June 2017. In his rookie season, Dunn played in 66 games, batting .262 with 19 home runs and 43 RBIs. Dunn received a single vote in 2001 National League Rookie of the Year voting, tying him for fourth place with Bud Smith.
In 2002, Dunn hit .249 with 26 home runs and 76 RBIs as well as a career-high 128 walks and a .400 on-base percentage. At mid-season, Dunn was hitting .300 with 17 home runs and 54 RBIs, earning him a selection to the 2002 National League All-Star team. In that game, Dunn hit a ball to center field that was a few feet from being a game ending home run (the game famously ended in a tie). He also walked in his only other plate appearance.
Dunn's 2003 season was a steep decline from his previous All-Star campaign as he hit just .215 with 27 home runs and 57 RBIs. Along with his struggles at the plate, Dunn led all major league outfielders in errors, with 10, and suffered a thumb sprain while attempting a diving catch in mid-August that forced him to miss the remainder of the season.
Dunn's most productive season came in 2004, when he posted career highs in batting average (.266), home runs (46), runs (105), hits (151), slugging percentage (.569), and on-base plus slugging (OPS) (.957). On September 30, 2004, Dunn once again got his name in Major League Baseball's record book. That day, Dunn struck out three times against Chicago Cubs right-hander Mark Prior, raising his season total to 191 and surpassing Bobby Bonds' single season strikeout record of 189, set in 1970. He finished the season with 195 strikeouts and had a strikeout percentage of 34.3%, both of which led all of MLB. He held the record until Ryan Howard broke it on September 27, 2007. On August 10, 2004, Dunn hit the longest home run in the history of Great American Ball Park, a 535-foot blast to straightaway center that went over the batter's eye and bounced off Mehring Way into a section of the Ohio River that is considered part of Kentucky. As of June 2025, it is the fourth-longest home run in MLB history and the longest since 1971.
Dunn's 46 home runs in 2004 were the fourth most in Cincinnati Reds history. That year, he joined Hall of Fame second baseman Joe Morgan as the only Reds players to score 100 runs, drive in 100 runs, and draw 100 walks in a single season.
Dunn's 2005 season was similar to the previous year, with a slight dip in production as he hit .247 with 40 home runs and 101 RBIs while once again leading in strikeouts (168) and strikeout percentage (30.9%). By reaching the 40 home run plateau for a second consecutive season, Dunn became the fourth player in Reds history to hit 40 home runs in multiple seasons.
Prior to the start of the 2006 season, Dunn signed a 2-year, $18 million extension that bought out his final two years of arbitration, as well as a club option for a third year in 2008. Dunn once again hit 40 home runs, but once again saw a decrease in his average (.234) and RBIs (92). For the third consecutive season, Dunn led all of MLB in strikeouts (194) and strikeout percentage (34.6%). He also led all major league outfielders in errors, with 12, and had the lowest fielding percentage among left fielders, at .960.
On June 30 of that season, Dunn made Cincinnati headlines with one of the biggest home runs of his career, a walk-off grand slam to cap a 9-run rally to beat the Indians, which kept the Reds tied atop the NL Central with St. Louis.