My engine ran backwards on me once. I was pushing a tree with my front end loader, and as I was pushing, I pressed the clutch just as the engine was about to die, and the tree sprung backwards and I let out the clutch again as the tree was pushing me backwards, and the engine cranked back up running backwards.
Black smoke came out of the air intake and it scared the crap out of me. I shut it off with the key within 2 seconds or so and called the mechanic. I didn't know what was going on. When I explained to him what happened, he knew right away what happened.
I was relieved when he said there should be no damage. There wasn't any.