From 2002 to 2004, Grinch was a graduate assistant under Gary Pinkel at the University of Missouri, and he completed his master's degree in educational leadership and policy analysis at Missouri in 2004.[5]
New Hampshire
Grinch's first regular assistant coaching job was at Division I-AA New Hampshire under Sean McDonnell. In 2005 and 2006, Grinch was the cornerbacks coach.[5] After a promotion, Grinch became the recruiting coordinator and coached the entire defensive secondary in 2007 and 2008. Chip Kelly was the OC at New Hampshire and Grinch learned the value of practicing fast from competing against him every day.[6]
Wyoming
Grinch spent three seasons at Wyoming as the recruiting coordinator and coaching the secondary. He coached cornerback Marqueston Huff who was drafted into 4th round of NFL and Tashaun Gipson would become a future NFL Pro Bowl safety.[6]
In January 2019, Grinch joined Lincoln Riley's staff at Oklahoma as defensive coordinator.[10] He spent three years with the Sooners and was able to help turnaround defense that finished 101st in scoring defense and 130th in passing defense, under former defensive coordinator Mike Stoops, who would be fired after giving up 48 points to rival Texas. In 2019, their defense allowed the fewest yards per game, ranking 20th. Oklahoma won the Big 12 championship and advanced to the College Football Playoff semifinals in the Peach Bowl.
USC
In November 2021, Grinch followed Riley after he was hired to be the next head coach at USC, serving in the same capacity as before.[11] At USC he inherited a Trojan defensive roster that in 2021 finished as one of the worst units statistically in program history, ranking 103rd in scoring defense and well below average in all other categories.[12] In his first year at USC, in 2022, the Trojans had the nation's best turnover margin. This marked a huge improvement over 2021, when the Trojans were ranked 74th in the country in the same category. The Trojans focused extensively on turnovers, ranking third in the country with interceptions from a dozen different players. Tuli Tuipulotu was named the Pat Tillman Defensive Player of the Year and unanimous All-American in 2022. They finished the season 11–3, losing to Utah in the Pac-12 championship game, eliminating them from national championship playoff consideration. Mekhi Blackmon was named All-America and drafted in the 3rd round of 2023 NFL draft.
In February 2024, Grinch joined Luke Fickell's staff at Wisconsin as co-defensive coordinator and safeties coach. The secondary thrived and ranked #14th in country of passing yards allowed.[15]
UCF
In December 2024, Grinch was announced as UCF's defensive coordinator following the hire of Scott Frost.[16]
Personal life
Grinch grew up in Grove City, Ohio and graduated from Grove City High School.[17] In 2003, he married Rebecca Blaser. They have two children.[7] He is the nephew of longtime Missouri head coach Gary Pinkel, under whom Grinch worked as a graduate assistant and safeties coach.[17]