Don't know if the Bats will be in town that Saturday (or if you can make it), but the "Thunder Over Louisville" Air Show (and amazing fireworks display) is April 20. It's a great time and a lot of other stuff going on in conjunction with it. It kickoffs the leaqdup to the Derby.
As a matter of fact, I just checked and they do play on 4/20, I might just have to make that one myself.
They play Indy (the Pirates AAAaffiliate) on Friday 04/19 (6:35PM) and Saturday 04/20 (2:05PM).