Since the birth of the VHS tape, video has been an important tool for athletes of all levels. American League designated hitters have long sneaked into the clubhouse in the middle of a game to watch their previous swings. And if you go to a sixth-grade basketball game, you’re almost certain to see a proud parent in the stands, hoisting a camcorder or — more likely these days — a smartphone.
But combine video with data on that phone, and now you have something. Sports-instruction apps are on their way to the pros — and those of us pretending or aspiring to be.