The act of presenting an interesting problem to a certain type of nerd, usually a physicist or a mathematician, while he/she is crossing the road, in such a manner that he/she becomes so occupied with it that he/she is soon run over.
First defined on xkcd
"There's a certain type of brain that's easily disabled. If you show it an interesting problem, it involuntary drops everything else to work on it. This has led to me to evolve a new sport: Nerd Sniping."