Prior to his inaugural season as a coach, Denning was a four-year starter for the Castleton University Spartans football program as a defensive lineman. He led all Castleton defensive linemen with 60 and 54 tackles in 2014 and 2015, respectively, while earning a spot on the Eastern Collegiate Football Conference (ECFC) All-Conference team both seasons. In 2015, Denning recorded a program-record 6.0 sacks and 13.0 tackles for a loss in 2015. The North Adams, Mass. native left Castleton with a career sacks record (13.0) and career tackles for a loss (27.5), while finishing sixth all-time in tackles with 204.