Thayer was more of a journalist than a poet. During his time at the San Francisco Examiner, he wrote some other ballads that appeared in the paper, but "Casey at the Bat" is the one that made him famous and that still gets read today.
That said, just because a poem is about Casey, that doesn't necessarily mean it's by Thayer. The poem inspired tons of alternative versions and offshoots. If you're curious about Casey-inspired poems, check out The Annotated Casey At The Bat by Martin Gardner. That should do the trick.