Talk about airing your dirty laundry!! Seriously though...
First of all, read the fabric care tag that's probably in the side-seam of the jacket. I assume it's machine washable. Is it a nylon kind of fabric? I would try a pre-treater like "Shout" or else rub some liquid detergent into the stain. This might help break up the stain, since I assume that the yellow on a softball is actually some kind of paint. Either way, pretest in an inconspicuous place to make sure the pretreater won't fade your fabric. Rub the stuff down into the stain, don't just squirt it on top of the fabric.
Good luck,
MOM