Hegman did not start playing football until his senior year at Northside High School in Memphis, Tennessee.

He was a teammate of Ed "Too Tall" Jones, and the starting middle linebacker on the school's 10–0 team, that won the black college football national championship in 1973.

[3] After his unusual entrance into the NFL in 1976, he spent most of his first four seasons playing special teams and as an outside linebacker backup to Thomas "Hollywood" Henderson and D. D. Lewis.

During Super Bowl XIII against the Pittsburgh Steelers, he made his most famous play, taking the ball from Terry Bradshaw and scoring on a 37-yard fumble return for a touchdown.

[8] Hegman played 12 years and started in 116 games, becoming a dependable player in the Cowboys defense for more than a decade.