Just read the book The Arm by Jeff Passan. Factual and informative, though Passan does not come right out and tell us what he thinks is the cause of the epidemic of UCL tears in baseball. He does confirm a fact that Dr. James Andrews has written and talked about at length, and it is this: In the 1990s, of all Tommy John surgeries performed, 0% were performed on teenagers; today, 57% of all Tommy John surgeries are performed on teenagers. That is a shocking increase. What changed in youth baseball from the 1990s to today? We all know, don’t we?