Well, I'd have the field as a big object, and the bases etc as limbs on the object. That would allow you to guage the position of the bases and the home base. It's actually really simple to get the guys running around the bases using a simple pointing system and a distance check to determine when the base has been reached.
For the Pitcher, I'd have an animated pitcher dude with a few different throws, then simply stick the ball to his hand until the animation frame that releases it - then you treat it as a projectile.
For the batter, I'd have a simple bar with a skill point - like a line with a bubble in the middle, the ball would fall down and you'd have to 'bat' when the ball is in the bubble, the bubble could be used to gauge the projectile qualities of the ball - a perfect hit resulting in a home run, or if the ball is too high it might get knocked really high up - making it easy to catch. That would be a nice way to handle it because you'd have a similar dilema as a real life batter, deciding when to actually go for a hit - because the pitchers throw style could determine the speed of the ball falling passed the bubble.
The fielding players would basically run after the ball or mark a base, pretty straightforward AI, because the AI difficulty would be determined by how accurate they are - and all the AI could easily be perfectly accurate in a game like this if you wanted.
I reckon a baseball game would be real easy in DB, and the engine for it would'nt need a total monster PC, not too many players, small field, relatively relaxed and skillful gameplay.
Why not give it a go Killercube?
Van-B

The nature of Monkey was irrepressible!.