Farmer made 11 MLB appearances for the Rangers during the first half of the 1979 season. A notable feud started between Farmer and outfielder Al Cowens — then with the Kansas City Royals — early in the season. On May 8, a Farmer pitch thrown in the top of the fifth inning fractured Cowens' jaw and broke several teeth, causing him to miss 21 games. Farmer later said that Cowens had attempted to steal signs from the catcher and thought the pitch would be a breaking ball away, but it was actually an inside fastball. At the start of the same game, Farmer had also hit Royals second baseman Frank White and broke his wrist, which kept him sidelined for a month.