Allen was born in Dallas, Texas and grew up in Humble, Texas. He attended Summer Creek High School and was a standout football player for the Bulldogs. As a senior, he recorded 112 tackles and three interceptions and was named the Defensive MVP of District 19-4A. He committed to play college football at Texas Tech over offers from Oklahoma, TCU, Kansas State, and Iowa State.
College career
Allen began his collegiate career at Texas Tech, redshirting his freshman season. As a redshirt freshman, Allen was the Red Raiders' second-leading tackler with 87 stops. After the end of the season, he was charged with second-degree burglary along with two teammates and ultimately expelled from Texas Tech. All charges were eventually dropped against Allen after agreeing to enter a pre-trial diversionary program. Following his dismissal, he transferred to East Mississippi Community College, where he was featured in the second season of the Netflixdocumentary seriesLast Chance U. Allen recorded a team leading 117 tackles with two sacks with an interception, a forced fumble, a fumble recovery and five pass breakups. Despite success on the field early in the season, he only originally received scholarship offers from Bowling Green and Troy due to his previous arrest. Allen later received offers from Ole Miss, Mississippi State and Marshall, but opted to return to Texas Tech to finish his collegiate career. Allen had a breakout junior season in 2017, with 92 tackles, 12 tackles for loss, and six forced turnovers. He was subsequently named to the All-Big 12 by Pro Football Focus and to the second-team All-Big 12 by coaches and media. As a senior, Allen made 73 total tackles, including 6.5 for loss, and was named first team All-Big 12.
Allen was drafted by the Los Angeles Rams in the seventh round of the 2019 NFL Draft. Allen signed a four-year $2,594,288 contract with a signing bonus of $74,288 on June 7, 2019. He was waived during final roster cuts on August 31, 2019, but was signed to the practice squad the following day.
On September 24, 2019, Allen was signed by the Oakland Raiders off the Rams practice squad. Allen made his NFL debut on October 6, 2019 against the Chicago Bears, playing eight snaps on special teams. He was waived on October 30 after appearing in two games for the Raiders.
Los Angeles Rams (second stint)
On November 4, 2019, Allen was signed to the Los Angeles Rams practice squad.
Jacksonville Jaguars
On December 10, 2019, Allen was signed by the Jacksonville Jaguars off the Rams practice squad.
