In To Kill a Mockingbird, how does Bob Ewell die?

Atticus believes that Jem killed Bob Ewell.  When Jem and Scout were on their way back from the Halloween Party, there was a scuffle between Jem, Scout, Bob Ewell, and a mysterious figure (believed to be Boo Radley).  Bob Ewell died as a result of that scuffle and being that Atticus only saw Jem as a result of it, he believed that Jem took Bob's life.