In baseball the players sometimes don't look like they are in shape, but they have to train in a special way.
Pitchers can't build hard upper muscle, it jams up their arm when they throw. But they do work on their legs to get a good push off the mound. But they are weak hitters, but at or slightly above average runners.
Power hitters need good arm power and upper back muscle. And large leg muscle to push the bat around. But are a little below average on running, usually they are in the outfield.
Number hitters (lead off) work on overall body without doing to heavy on the weights, they need break away running and the ability to put the ball in play, not go deep. They are not great power hitters, don't expect them to knock one out. But they have good speed and play a lot of infield positions, or center field.
So baseball has a lot of different players. They all don't just run up and down a court doing the same thing. There is a lot of thought about what players to play and then what position etc...