I've seen the expression "leave it all on the road" on this site and in propaganda by various campaigns, all of them for Democrats.
But I just hopped onto the information superhighway to see what doing a google in the intertubes would net me and came up with less information than that with which I started. So I'm asking you, the people most likely to know: what does "leave it all on the road" mean and what exactly are its origins? What does the pronoun "it" refer to? What does the metaphor "road" represent? Does "leave" means that "it" can never be retrieved? Those are my questions. Thank you and good night.
UPDATED I: Wow, that tells you something! This has been up for a couple minutes and not a single post. This seems to indicate that no one knows the origin of "leave it all on the road." It must have been placed in our brains by a divine process. Intelligent design and idea implantation is real!
UPDATED II: So it's a sport metaphor. That's good to know so I know to avoid using it.