“Mack Wrestles,” co-directed by Taylor Hess and Erin Sanger, takes the audience behind the scenes as Mack Beggs, a gifted athlete from Euless, Texas, struggles against the outside forces that stigmatize transgender athletes. Wrestling is brutal enough. There are the demands for strength and speed and stamina, the hours bathed in sweat, the knowledge that your opponent wants to wipe the mat with you. Those were the very reasons, though, that Beggs loved the sport—it gave him a sense of purpose and a sense of self. Despite all the turmoil, this poignant film makes one thing perfectly clear: If life were a wrestling match, the referee would be raising Mack’s arm at the end.