The Indians selected Allen in the 23rd round of the 2011 MLB draft. Allen signed with Cleveland and spent 2011 with four teams in the Indians' farm system, but spent the majority of the season with the Mahoning Valley Scrappers of the Class A-Short SeasonNew York-Penn League, pitching to a 3–1 win-loss record with a 2.14 earned run average in 14 games. Between the four teams, he was 5-1 with a 1.65 ERA, and 75 strikeouts in 54.2 innings, averaging 12.3 strikeouts per 9 innings. The following year he spent most of the season with the Columbus Clippers of the Class AAAInternational League, going 3–2 with a 2.27 ERA in 24 games. Pitching for three minor league teams, he was 3-2 with three saves and a 1.87 ERA, and 53 strikeouts in 43.1 innings, averaging 11.0 strikeouts per 9 innings. He was named the Cleveland Indians' Minor League Pitcher of the Year after the season. After the 2012 season Baseball America ranked him the 5th-best prospect and best curveball in the Indians organization, and the 13th best-prospect in the International League.
Major leagues
Cleveland Indians
On July 20, 2012, Allen made his Major League debut for the Cleveland Indians after being called up from Columbus He pitched an inning of relief giving up two walks, no runs, no hits, and one strikeout. He struck out Baltimore Orioles third baseman Mark Reynolds for his first career strikeout. In 2013, Allen went 6–1 with a 2.43 ERA and 88 strikeouts in 70.1 innings, averaging 11.3 strikeouts per 9 innings. His 77 games pitched was second in the American League, trailing only Joel Peralta's 80, and he was 2nd in the league in errors committed by a pitcher, and 8th in wild pitches. He tied for 6th in the 2013 BBWAAAL Rookie of the Year voting. After multiple struggles by closerJohn Axford early in the 2014 season, Allen was moved into the closer role. Allen finished the season with 76 appearances, a 6–4 record with a 2.07 ERA, 91 strikeouts, and 24 saves in innings, averaging 11.8 strikeouts per 9 innings. For the 2015 season, Allen pitched in 70 games, leading the American League with 58 games finished, while recording 34 saves, 99 strikeouts, and a 2.99 ERA in innings, averaging 12.9 strikeouts per 9 innings. In 2016, he had 32 saves in 35 save opportunities, going 3–5 with a 2.51 ERA. He struck out 87 batters in 68 innings, averaging 11.5 strikeouts per 9 innings. In 2017, he had 30 saves in 34 save opportunities, finishing the season with a 3–7 record and a 2.94 ERA. He struck out 92 batters in innings, averaging 12.3 strikeouts per 9 innings. With his 141st career save in July 2018, Allen broke Bob Wickman's franchise record for saves. Allen lost his closer role to Brad Hand after struggling in the month of August. He ended the season with 27 saves in 32 save chances in 70 appearances, as he was 4-6 with a 4.70 ERA, with 80 strikeouts in 67 innings, averaging 10.7 strikeouts per 9 innings. Through 2018, his 149 career saves were 9th of all major league active pitchers, tops of all major league pitchers under 30 years of age, and tops of all Cleveland Indians pitchers ever. He became a free agent after the 2018 season.
Los Angeles Angels
On January 20, 2019, Allen signed a one-year, $8.5 million contract with the Los Angeles Angels. He began the season as the Angels closer, going 4/4 for the first couple of weeks of the season despite control issues. He was removed of the closer role on April 24 and later was placed on the injured list with a lumbar strain. He was designated for assignment on June 15 after compiling a 6.26 ERA 25 games, and was released on June 18.
Minnesota Twins
On June 22, 2019, the Twins signed Allen to a $500,000 minor league contract for the remainder of the 2019 season. He was released on July 31, 2019.
On February 7, 2020, Allen signed a minor league deal with the Texas Rangers. Allen was released by the Rangers organization on July 24, 2020.
Chicago Cubs
On July 31, 2020, Allen signed a minor league contract with the Chicago Cubs.
Personal life
Allen married Mallory Rundquist in November 2015. The couple have a son, who was born in 2017. His twin brother, Chad, played baseball for the University of West Florida.
