The acronym SAC stands for 'Runs Batted In Producer, ' which is a baseball statistic that measures the number of runs a batter produces for their team. It is often abbreviated as RBI. The term 'FLY' refers to a type of hit in baseball, where the ball is hit high into the air and usually lands outside the infield. Therefore, the crossword solution 'RBI Producer' is referring to a batter who is able to hit FLY balls that result in runs batted in.