Heathcliff is understandably wary of jogging out to the mound: it appears to be made of quicksand. To remedy this, he steals an elephant-shaped balloon from the parade and floats it out to the mound, which will completely stop him from sinking once he starts pitching.
Softball?!? Heathcliff is a pussy. And I mean that in the derogatory way, not that he's a cat, or better, a vagina. It probably isn't even fast pitch. At least that'd be somewhat respectable.