Clay for high traffic areas around plates and mounds, batters boxes, catcher and ump areas.
For the infield, you'll want a clay and sand mix which any landscape supply will have. I would ask to have it donated before you pay for it.
If you can, leave the grass on the infield. The dirt on the infield is high maintenance so the less dirt, the better. Wet dirt is what cancels games, not the rain. If you have to take it off, kill it first with some round up. If you don't want to rent a bobcat, you can get the dead stuff off with a sod cutter or even a lawn mower at the lowest setting and a weed eater.
Jon
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