In 2021, Arnold redshirted and did not play in any games.[6] In week six of the 2022 season, Arnold recorded his first career interception off a pass by Haynes King before breaking up a pass in the end zone on the final play of the game to help the #1 Crimson Tide survive Texas A&M 24–20.[7][8] In week 11, Arnold tallied ten tackles, two pass breakups, and a fumble recovery, as helped Alabama beat Ole Miss 30–24.[9][10] Arnold finished the 2022 season with 45 tackles with one going for a loss, eight pass deflections, an interception, and a fumble recovery.[11][12] For his performance on the season, Arnold was named a 2022 Freshman All-American by FWAA.[13][14] In 2023, Arnold was named a first-team All-American after recording 63 tackles, 5 interceptions, a sack, and forced fumble.[15] He declared for the 2024 NFL draft following the season.
The Detroit Lions selected Arnold in the first round (24th overall) of the 2024 NFL draft. The Detroit Lions initiated a trade that sent their first (29th overall) and third round (73rd overall) picks to the Dallas Cowboys in order to receive the 24th overall pick to draft Arnold and also received a seventh round pick in the 2025 NFL Draft.[18]
On June 13, 2024, the Detroit Lions signed Arnold to a four-year, $14.34 million contract that includes a signing bonus of $7.25 million and is fully guaranteed upon signing.[19]
Personal life
Arnold has a close relationship with Terry Saban, the wife of Nick Saban, describing her as "like a best friend" and "a second mother".[20][21]