He played his first three seasons of college football for the Oklahoma Sooners, receiving first-team All-Big 12 honors in 2020, and his final two with the South Carolina Gamecocks.

[3] In his final season at Pinnacle, Rattler starred in a Peter Berg-directed Netflix sports documentary series called QB1: Beyond the Lights.

Rattler was later suspended for violating a district code of conduct, and was ineligible to play for the rest of the season due to cheating.

[4] He initially said he had a sprained MCL, but the school administration later advised him not to speak of the nature of the code of conduct violation.

[16] On September 26, Rattler tied the Oklahoma record for most touchdown passes through two weeks with 8, set by Sam Bradford in 2008.

[20] As the starting quarterback, he led the Oklahoma Sooners to a 6th consecutive Big 12 Championship, winning 27–21 over Iowa State.

[21][22][23] However, during Oklahoma's match-up against Texas, Rattler was benched during the second quarter for Caleb Williams and would not play the rest of the season.

[25] Ole Miss, UCLA, Arizona State, Nebraska, Pitt, Auburn, Missouri, and Oregon were among the schools that pushed for Rattler the hardest.

[28] South Carolina tight ends Austin Stogner and Jaheim Bell have also been cited as influencing Rattler's decision.

[32] His performance in the first ten games of the season was described as "underwhelming": he averaged 198 passing yards and threw more interceptions than touchdowns.

He fumbled twice, one of which was returned for a touchdown, before leaving the game due to a hip injury late in the fourth quarter.

[51] In Week 15 against the Washington Commanders, Rattler replaced starting quarterback Jake Haener in the 2nd half.

Rattler completed 10 of 21 passes for 135 yards and a touchdown to Foster Moreau with no time left on the clock, which brought the score within a point.