Allen played in 15 games during his freshman season with the Clemson Tigers and was used primarily as an in-line blocker.[4] He caught 16 passes for 247 yards and four touchdowns in his sophomore season.[5][6] Allen had 28 receptions for 208 yards and three touchdowns as a junior.[7][8] He was named third-team All-Atlantic Coast Conference as a senior after catching 39 passes for 443 yards and five touchdowns.[9]
Allen was selected by the Los Angeles Rams in the fifth round, 175th overall, of the 2023 NFL draft.[12] He played in 15 of 17 games during the regular season. In Week 14, Allen caught a season-high four passes for 50 yards, including a 7-yard pass from quarterback Matthew Stafford for his first career NFL touchdown in the Rams' 37–31 overtime loss to the Baltimore Ravens.[13] Against the San Francisco 49ers in Week 18, Allen made his first professional start, catching four passes for 25 yards in the Rams' 21–20 victory.[14] In an NFC Wild Card Game at Detroit, Allen caught two passes for 28 yards in the Rams' 24–23 loss to the Lions.[15]