Castillo played for the San Antonio Gunslingers of the USFL from 1984–1985, mainly on special teams.[2] In 1984, Castillo saw action in six games, making four tackles and three assists. In 1985, Castillo played in seven games, making eight tackles and registering three assists on a 5–13 club.
The Philadelphia Eagles hired Castillo as an offensive assistant in 1995 under Ray Rhodes.[1]In1996, the Eagles drafted Jermane Mayberry, an offensive lineman Castillo coached at Texas A&M University–Kingsville, in the first round of the 1996 NFL draft. Castillo was promoted to tight ends coachin1997, and switched to coaching the offensive line in 1998. When Andy Reid was hired as the head coach of the Eagles in 1999, he retained Castillo on the coaching staff.[1] Mayberry earned a Pro Bowl berth in 2002, and said Castillo "molded me into the player I became." Castillo coached the offensive line for thirteen seasons, from 1998 to 2010.
Castillo became the defensive coordinator for the Eagles following the firing of Sean McDermott on February 2, 2011.[4] The hiring was met with surprise by players, fans, and members of the media primarily because Castillo had not coached the defensive side of the ball since he was at Kingsville in 1989.[5][6] Castillo was fired on October 16, 2012.[7]
On January 21, 2013, Castillo was hired as a consultant by the Baltimore Ravens. At the time of the hiring, the Ravens were preparing to play in Super Bowl XLVII.[8] Castillo would officially join the coaching staff for the 2013 season as the run-game coordinator and held the job for one season, before serving as the offensive line coach from 2014 to 2016.[9]
In 2017, Castillo was hired by the Buffalo Bills to become the offensive line coach and run-game coordinator under new head coach Sean McDermott.[10] He served two seasons with the Bills before being dismissed following the 2018 season.[11]
Castillo joined the Michigan Wolverines coaching staff as an offensive analyst for the 2019 season. As part of his duties, Castillo worked with Michigan offensive line coach Ed Warinner.[12]
Castillo was hired by the Chicago Bears as offensive line coach on January 5, 2020. The move reunited him with head coach Matt Nagy, whom he worked with in Philadelphia.[13] He was not retained by the team following the firing of Nagy after the 2021 season.
Castillo fractured his left tibial plateau after he was hit by a utility truck outside of Veterans Stadium on August 17, 1998.[15] His hometown of Port Isabel declared July 4, 2009, to be "Alex Castillo Day".[16]
