I heard Ode to Billy Joe today. And the same questions came to me as they do every time I hear the song: What was thrown off the Tallahatchie Bridge? Was it the narrator and Billy Joe on the bridge? And, of course, why did Billy Joe jump?
I think that that it was a forbidden romance between the narrator and Billy Joe and that they threw off a Wedding Ring, because she knew she couldn't marry him because he was from the wrong side of town, Choctaw Ridge. As the song put it, "Seems like nothin' ever comes to no good up on Choctaw Ridge." Left by the girl he loved, he kills himself.
Here is an link with some theories:
The Mystery of Ode to Billy Joe
Here's the song: