[2] He attended Lawton Chiles High School where he was a football player, totaling 93 tackles, 24 tackles-for-loss (TFLs) and 12 sacks as a senior.
[3] He was a top-250 recruit and a four-star prospect, ultimately committing to play college football for Florida State, the school his father had attended.
[3][4][5] As a true freshman at Florida State in 2018, Gainer suffered a broken foot and redshirted, having appeared in four games during the season.
[2] Gainer transferred to the North Carolina Tar Heels for his final season in 2023, ending his stint at Florida State having made 210 tackles, 19 tackles-for-loss, six sacks and five forced fumbles.
[2] After going unselected in the 2024 NFL draft, Gainer signed with the Las Vegas Raiders as an undrafted free agent.