From The Teammates: A Portrait of a Friendship by David Halberstam:
[Bobby] Doerr remembered his first glimpse of Ted. It was June 1936, and the original Hollywood Stars had just moved to San Diego and been reborn as the Padres, after Bill Lane, the owner, balked at a 100 percent rent increase for Wrigley Field, the ballpark the Stars and the Los Angeles Angels shared. Some San Diego businessmen induced Lane to move the team south to what then was a city of only 200,000 people. It was right before a game, just as the regulars were taking batting practice, when Williams, who had been playing for a local school, Herbert Hoover High, was brought in for a tryout.
“I was standing right near the batting cage,” Doerr remembered, “on the first-base side — I don’t know why I was there, but I remember the scene distinctly. And here is this kid, and he is really skinny. You wanted to laugh — no one that thin could possibly hit. ‘Let the kid hit,’ Shellenback is saying, because he’s been told that by the owner, Bill Lane, who wants to look at Ted. The veterans are all grumbling — you know, we all wanted our batting practice swings. No one thinks he can be a ballplayer, he’s much too thin, and we’ve got a game in an hour or two, and he’s not even going to play with us. So we’re impatient and there’s a lot of resentment, a lot of muttering. And then he started to swing. And we all remembered that swing. You paid attention to the swing. He hit six or seven balls very hard, and all the veterans are starting to watch, and it’s getting very quiet, and I remember one veteran player saying, ‘That kid is going to be signed before the week is out.'”
Dominic DiMaggio remembered a similar scene. “It was my first year in the league. It was early in the season. I was playing for the San Francisco Seals, and we were playing San Diego. I wasn’t starting yet. Brooks Holder was our centerfielder, very fast, but he couldn’t catch the ball, so there was going to be a place for me. Lefty O’Doul was our manager. The other guys, the San Diego players, are taking batting practice, and eventually Ted comes up to take his swings. And suddenly Lefty, who was a great hitter, and a great hitting instructor, jumps up from our dugout and goes to the other side of the field, near their dugout. That’s very unusual — you just didn’t do that in those days. And he waits there, and finally Ted finishes his swings, and Lefty calls him over, and they talk for a little bit. Maybe twenty or thirty seconds. And then Lefty comes back to our dugout. And we’re all sitting around, and someone asks him, ‘Skip, what was that all about?’ And Lefty says, ‘That kid is one hell of a hitter. And all I told him was, “Don’t let anyone ever tamper with your batting stroke. Just don’t let anyone ever touch you.”‘”
It was just his swing and his natural talent. He broke down hitting to a science with mathmatical probabilities… Ted was very smart.
He also apparently had amazing vision. Ron Luciano (in “The Umpire Strikes Back”, IIRC) tells about a time when he (Luciano) was the plate umpire and Williams hit a ball. Williams was able to tell Luciano where on the ball his bat had made contact. Luciano verified the position by the scuff mark on the ball when it was thrown back in to him.