Jacob Tanner Diekman (born January 21, 1987) is an American professional baseball pitcher in the Atlanta Braves organization.

He has previously played in Major League Baseball (MLB) for the Philadelphia Phillies, Texas Rangers, Arizona Diamondbacks, Kansas City Royals, Oakland Athletics, Boston Red Sox, Chicago White Sox, Tampa Bay Rays, and New York Mets.

Eventually, Diekman joined an American Legion baseball team, playing in the summer with other players from Wymore and several surrounding towns, which he called "the best experience of my life ... so much fun.

"[1][2] Concurrently, Diekman worked full-time at a lawn mower factory, to earn money to pursue a post-secondary education.

[1] Between 2007 and 2010, he pitched in the lower levels of the Philadelphia Phillies' Minor League system initially as a starter, and subsequently as a reliever.

[5] Around that time, he also, at the suggestion of the same minor league pitching coaches who converted him to relief, lowered his release point to his current low angle.

[4] He spent the 2011 season with the Double-A Reading Phillies, accruing a 0–1 record and a 3.05 ERA and 3 saves in 53 games.

[7] After receiving praise from Phillies' pitching coach Rich Dubee for his performance in spring training,[8] Diekman opened the 2012 season with the Triple-A (AAA) Lehigh Valley IronPigs.

He was added to the Phillies' 25-man Major League roster on May 11, and four days later recorded a win against the Houston Astros in his MLB debut.

[9] He finished the year an established lefty specialist, and had a 3.95 ERA, though walked 6.6 batters per 9 innings, and was erratic in his control.

[10] Entering 2013, Diekman was expected to be a key part of the Phillies bullpen after his success in 2012, however he did not break camp with the big league club, beginning the season in AAA.

[12] Early in the season, Diekman emerged as a reliable reliever in the Phillies' bullpen, and was used extensively by manager Ryne Sandberg.

[14] On September 1, 2014, Diekman was one of four pitchers who combined for a no-hitter in the Phillies' 7–0 win over the Atlanta Braves in Turner Field.

There was excitement from both Phillies' personnel and writers that the bullpen could remain solid for a long time because of young pitchers such as Diekman, Ken Giles, and Justin De Fratus.

[19] Overall, Diekman emerged as a name to be mentioned among the "elite" relievers of the National League, but was overused against right-handed batters, which hurt his statistics.

[20] On July 31, 2015, Diekman was traded to the Texas Rangers along with Cole Hamels in exchange for Matt Harrison, Nick Williams, Jorge Alfaro, Jake Thompson, Alec Asher, and Jerad Eickhoff.

[27] In 48 relief appearances with the 2019 Royals, Diekman accrued a 4.75 ERA and an 0–6 record while striking out 63 batters in 41+2⁄3 innings.

[28] On September 6, Diekman pitched in a suspended game between the Athletics and Detroit Tigers that originally started on May 19, allowing a double in a scoreless inning.

[32][33] On August 1, 2022, Diekman was traded to the Chicago White Sox for catcher Reese McGuire and Taylor Broadway.

[34] In 26 relief appearances through the end of the season, Diekman compiled an 0–3 record with a 6.52 ERA while striking out 28 batters in 19+1⁄3 innings.

[33] In 2023, Diekman made 13 appearances for the White Sox, struggling immensely to a 7.94 ERA with 11 strikeouts in 11+1⁄3 innings pitched.

Diekman has sought therapy to cope with the loss of his mother, and meditates and thinks about her during "The Star-Spangled Banner" prior to each game.