Every Sunday, Boston Globe photographer Stan Grossfeld asks the subject of one of his photos to explain what's happening in the shot.

Who’s up today: Twins baserunner Alexi Casilla (partially obscured), though standing on the base, is called out by umpire Brian O’Nora for interfering with Tigers shortstop Jhonny Peralta when Peralta backs into him while pursuing a popup at Comerica Park, Detroit, Sept. 22, 2012.