Education
After redshirting in 2010, he played as a reserve defensive tackle in his 2011 and 2012, picking up 9 total tackles and one tackle for a loss.
In 2013 Grissom saw his first career start come against ULM Warhawks in which he recorded two tackles. His first interception came on October 12 against the Texan Longhorns, which he returned 54 yards for a touchdown. In the Sugar Bowl against Alabama, Grissom recorded 2.5 sacks, broke up a pass, and recovered two fumbles.
He returned one of these fumbles for an eight yard touchdown and had a total of 34 return yards.
As a senior at Oklahoma, Grissom was named an honorable mention for the All-Big 12 after recording 39 tackles and 3.5 sacks on the year.
Over his four seasons at Oklahoma, he registered 88 tackles, 8 sacks, 2 forced fumbles, 3 fumble recoveries and 2 interceptions while playing in 39 games with 12 starts.