If you recall the initial days of the juiced era, big league batting practice often erupted into a powerful display of one deep majestic drive after another. But gawking at Fred McGriff and Gary Sheffield launching 500 foot home runs wasn't the reason I sped down I-5... The real reason I was there was to observe Tony Gwynn take batting practice. It is a rare treat when you realize in the moment you are witnessing someone very special do something better than everyone else on the planet. Watching Tony slash line drive after line drive into left center field hours before the game started was a study in repetitive muscle memory and single minded dedication.
From George Will's 1990 book Men at Work:
Early in the 1989 season Tony Gwynn hit home runs in consecutive games and was even more displeased with his hitting than he generally is. The second home run came after an afternoon spent toiling to remove flaws in the way he had swung the bat in the game in which he hit the first one. He knew the flaws were there. In fact, the home run was evidence that he was not hitting the pitches he wanted to hit in the way he wanted to hit them. So the afternoon before the night when he hit the second home run , he went to work early, several hours before the game.
The previous night he had hit two balls hard. One pleased him, the other distressed him. The pleasing one was an out, the distressing one was a home run. When he hit the ball hard for an out, as he started his stride forward his hands moved in the opposite direction. They came back so he could keep the bat backlog enough to "inside out" the ball to left field, lashing a line drive that was caught by the left fielder. To "inside out" is to sweep the bat through the strike zone at a slight angle, from the back inside portion of the plate toward the outside front portion. When a left handed hitter does that, he has power to the left side of the diamond.
On the home run swing, his hands came forward too soon. That is what he means by being "out in front". He drive the ball to right field. Sure, it went over the fence, but he knows that over the course of the long season, hitting the ball that way is a recipe for the sort of frustration he experienced in 1988.