Simmons redshirted his first year at Clemson in 2016. As a safety in 2017, he played in 14 games, recording 49 tackles and one sack.[4] In 2018, he converted to linebacker.[5] In 15 games, Simmons had 97 tackles, 1.5 sacks and one interception.[6][7] He returned to Clemson in 2019 rather than enter the 2019 NFL Draft.[8] Simmons received the Butkus Award as the nation's best linebacker for his performance that year.[9] After graduating in December 2019 with a degree in sports communication, Simmons announced that he would forgo his senior year by declaring for the 2020 NFL Draft.[10][11] During his time at Clemson, Simmons was noted for his positional versatility, taking snaps at linebacker, defensive end, cornerback, and safety.[12][13]
Despite playing only five snaps in Week 7 against the Seattle Seahawks on Sunday Night Football, Simmons recorded his first career interception off Russell Wilson with a minute left in overtime, helping the Cardinals win 37–34.[20]
Simmons entered the 2021 season as a starting inside linebacker. He started all 17 games, finishing third on the team with 105 tackles, 1.5 sacks, four forced fumbles, and seven passes defensed.
In Week 7 against the New Orleans Saints, Simmons had five tackles, and a pick-six in the second quarter in the 42–34 win.[21]
