Known for his toughness, the 6-foot-5, 250-pound Hrivnak left Johnstown to play football at Purdue, where he was a defensive end from 1970-72 and Big Ten All-Conference selection for Bob DeMoss' Boilermakers in 1971. Hrivnak also played tight end while at Purdue.
Hrivnak certainly caught the eye of NFL franchises and was drafted the the second round of the 1973 draft with the 48th overall selection by the Chicago Bears. Hrivnak was drafted before Hall of Fame quarterback Dan Fouts and Dallas Cowboys standout defensive end Harvey Martin.
He played four seasons with the Bears (1973-76) and started 11 games during his career. He was released by the Bears in 1977 after spending the 1976 season on injured reserve because of an Achilles tendon injury.