Prior to his officiating career, he was a college football player at Upper Iowa University.
Nemmers also has master's degrees in physics and chemistry, which he received at East Texas State University in Commerce, Texas and in educational administration from Northern Illinois University in DeKalb, Illinois.
Nemmers began his NFL officiating career in 1985 as a side judge, and was assigned Super Bowl XXV in 1991, his final game at that position before being promoted to referee for the start of the 1991 NFL season after Jerry Seeman and Jim Tunney announced their retirements.
He was the referee in the January 6, 2002, game that saw Dallas Cowboys running back Emmitt Smith accumulate 1,000 yards rushing in 11 consecutive seasons, breaking a record shared with Detroit Lions running back Barry Sanders.
[2] In another memorable moment, he was the referee in the November 27, 2005, game that saw New York Giants punter Jeff Feagles set the NFL record for consecutive games with 283, breaking the record held by Minnesota Vikings defensive end Jim Marshall.