On July 24, 1973, Kassulke suffered a motorcycle accident on the way to training camp that left him paralyzed from the waist down.[1][2]
After his playing career, Kassulke worked with Wings Outreach, a Christian Ministry to the disabled.[3]
Kassulke was immortalized in NFL lore by NFL Films' official highlight film for Super Bowl IV. Kansas City Chiefs coach Hank Stram, who was wired for sound by NFL Films executive producer Ed Sabol, noted the confusion in the Vikings' defense due to the Chiefs' shifting offense and quipped, "Kassulke was running around there like it was a Chinese fire drill".