Gailen was signed in 2011 and 2015 by the
Los Angeles Angels.
Wichita Wingnuts On July 28, 2008, playing for the
Wichita Wingnuts, he was named the
American Association Batter of the Week.
Chico Outlaws In 2009, Gailen batted .355 with the
Chico Outlaws of the
Golden Baseball League, and was the youngest batter in the top 10 in batting in the league. In 2010, he batted .387. (finishing 2nd in the league to
Larry Bigbie in batting average)/.480 (3rd in the league)/.603 for Chico, and was a league All Star. He played center field and batted leadoff for the Saltdogs, and also led the league in on-base percentage (.479) and slugging percentage (.622).
Los Angeles Angels Gailen was then signed to a minor league contract by the
Los Angeles Angels in July 2011, and played for the Double–A
Arkansas Travelers of the
Texas League, replacing
Mike Trout who had just been called up.
Toronto Blue Jays In August 2013, he was signed to a minor league contract by the
Toronto Blue Jays, as Gailen was leading the Atlantic League in doubles and walks while playing in 113 games for the Lancaster Barnstormers. He then played in 46 games for the
Venados de Mazatlan in the
Mexican Pacific Winter League. In 2017, Gailen began the season back with the Lancaster Barnstormers.
Los Angeles Dodgers Gailen signed a minor league contract with the Los Angeles Dodgers on June 25, 2017, and was assigned to the Double–A
Tulsa Drillers in the
Texas League. In 49 games for Tulsa, he hit .300/.369/.500. In 126 games he batted .282/.378/.511 and led the Atlantic League in home runs (28; one short of the franchise record) and RBIs (91), while coming in second in walks (72). He was named an All Star for the third time.
Los Angeles Dodgers (second stint) On January 22, 2019, Gailen signed a minor league contract with the
Los Angeles Dodgers. Playing for the Triple-A
Oklahoma City Dodgers in 2019, he batted .250/.321/.396 with one home run and six RBI. Gailen elected free agency following the season on November 4. On January 9, 2020, Gailen re-signed with the Dodgers organization on a minor league contract. He did not play in a game in 2020 due to the cancellation of the minor league season because of the
COVID-19 pandemic. Gailen was released by the Dodgers organization on July 1.
Melbourne Aces On October 3, 2020, Gailen signed a contract with the
Melbourne Aces of the
Australian Baseball League for the 2020-21 season.
Lancaster Barnstormers (fifth stint) On March 24, 2021, Gailen signed with the
Lancaster Barnstormers of the
Atlantic League of Professional Baseball for the 2021 season. In 2021 he batted .279/.421/.519 with 18 home runs, 72 RBI, and 68 walks (7th in the league) in 287 at bats for Lancaster. He became a free agent following the season. ==Coaching career==