I like it.
Some may say you could use a comma after "ball," but you don't need it. "There was no ball" is a complete sentence, and what comes after the "so" conjunction is a complete sentence, so technically you could put one there, but when you have an intro clause that is short like this it sometimes flows better without the comma -- and one is not required.
I think it reads much better without the comma, so i would omit it, but keep the one after "trees," because it makes for a nice pause there. You don't want the reader rushing into the next sentence, as thought the sentences were crashing into each other. Just my thoughts.
Also, and this may be me being weird, but the comma adds a little more emotional attachment between the speaker and Jenny. It's as if the speaker paused for a half-second before getting to imagining Jenny pitching to him, because it's meaningful. You run them together without the comma and it doesn't seem to matter as much.