John Richard Gelnar is an American former Major League Baseball pitcher.
Gelnar attended the University of Oklahoma.
He signed with the Pittsburgh Pirates as an amateur free agent in 1963. His contract was purchased by the Kansas City Royals from the Pirates after the 1968 season, but he was traded by the Royals with Steve Whitaker to the Seattle Pilots for Lou Piniella prior to the 1969 season. He was traded by the Brewers with José Herrera to the Detroit Tigers for Jim Hannan in 1971.