Playing all 13 games, starting 7, Allen recorded a total of 58 tackles with one sack and two tackle for loss. During his sophomore season he ranked second on the team in tackles with 81 only behind Brandon Bell. Had six tackles and one forced fumble vs Georgia in the 2016 TaxSlayer Bowl. In his junior season he ranked No. 16 in the Big Ten Conference with 7.9 tackles per game. No. 3 in the Big Ten and tied for No. 30 in the Football Bowl Subdivision (FBS) with two fumble recoveries. The 22-tackle effort vs. Minnesota ranked No. 3 on the FBS single-game list in 2016 (24 - Obi Melifonwu, UConn & Rodney Butler, NMSU).[3] In 2016, Allen also blocked the field goal that Grant Haley would return for a touchdown to upset No. 2 Ohio State, which became known as the Block Six.
The Pittsburgh Steelers selected Allen in the fifth round (148th overall) of the 2018 NFL draft.[7] Allen was the 15th safety drafted in 2018.[8] On May 10, 2018, the Steelers signed Allen to a four-year, $2.75 million contract that includes a signing bonus of $292,637.[9]
On August 31, 2019, Allen was waived by the Steelers and was signed to the practice squad the next day.[10][11] On December 20, he was promoted to the active roster.[12]
Allen was moved to linebacker for the 2020 season, and signed a one-year contract extension with the team on March 9, 2021.[13]
On March 15, 2022, the Steelers placed an original-round restricted free agent tender on Allen. He was released during final roster cuts on August 30.[14]