Tommy john surgery is the repair of ulnar collateral ligament of elbow. It is named after the pitcher from LA dodgers to get this surgery done in 1974 for the first time.
This is a very big topic with lot of myths like after surgery you could throw even faster and harder which has been proven completely wrong.
Recently as the need for speed has risen among young athletes these surgeries are becoming more common.
Not only the need for throwing hard but also doing so without proper mechanics, without proper warm up and proper conditioning is also a contributing factor.