During his career, Demmas was assigned to four Super Bowls (XIII, XVII, XXV, and XXVIII), all as an umpire.
Demmas was an executive in the National Football Foundation (NFF), and became head of its Middle Tennessee chapter.
Demmas worked much of his career as the umpire on the crew of a fellow AFL official, referee Ben Dreith.
During the fourth quarter of Super Bowl XIII, Dallas Cowboys safety Charlie Waters collided with Demmas as he was moving into position to tackle Pittsburgh Steelers running back Franco Harris.
Harris scored a touchdown on the play, giving the Steelers a 28–17 lead, and Pittsburgh went on to win the game, 35–31.