As Dr F noted in his comment:
Sain was indeed a pitching coach and according to the writings of Furman Bisher of the Atlanta Journal-Constitution, he was the best pitching coach ever.
I give to you a few excerpts from the article:
Higher praise came from higher authorities, like this celestial endorsement from Jim Brosnan, who could write as well as pitch. "Johnny Sain did for pitching in the '60s what Babe Ruth and the lively ball did for hitting in the '20s," which is just about as unlimited an endorsement as a fellow could make.
But Jim Bouton topped Brosnan, before he turned informant and wrote his tell-all book on players and their sinful ways. "Johnny Sain is the greatest pitching coach who ever lived," he said.
Sain distinguished himself by developing 20-game winners by the herd, Whitey Ford, Ralph Terry, Mudcat Grant, Jim Kaat, Earl Wilson, Denny McLain, Wilbur Wood, Stan Bahnsen and Mickey Lolich among them.
I recommend reading the entire article - the man knew his craft and how to share it with others.
A tip of the hat to Dr F for bringing this aspect of Mr. Sain's baseball career to light.