As freshman in 2018, Lacy redshirted and saw no game action at Oklahoma State.[6] The following year, he started all 10 games in which he appeared, missing three due to injury, totaling 20 tackles, including two for a loss, with one sack and two pass breakups.[4][7] In 2020, he remained a starter and was named honorable mention all-conference after leading the team's defensive line with 32 tackles and eight TFLs, additionally posting four sacks and five quarterback hurries.[2][8]
Lacy earned a second honorable mention all-conference selection in 2021, additionally being named to their first-team All-Academic squad as he posted 34 tackles, 11 for-loss, and 3.5 sacks.[4] He also recorded eight hurries, the fifth-best in school history since they started tracking the statistic in 1982.[4] His senior season in 2022 was cut short due to injury, and he finished it with 17 tackles, five quarterback hits and three sacks.[4] Lacy finished his stint at Oklahoma State with 113 tackles, 30 for-loss and 11.5 sacks while appearing in 44 total games.[9]
Lacy was selected by the Jacksonville Jaguars in the fourth round (130th overall) of the 2023 NFL draft.[12][13][14] He appeared in 15 games and posted 12 tackles and a pass deflection in his first season.[15]