Police around the nation are on high alert for a new and dangerous trend among urban teenagers: the "knockout game," in which teens knock out unsuspecting strangers for the fun of it, in incidents that are sometimes captured on video. Jeff Rossen reports on the spread of the game nationwide, including to New York City, where police are investigating at least seven attacks. Read the full 'Today' story here, or watch the video.
More from NBC News Investigations:
- US officials accused by socialite Jill Kelley of leaks as part of 'smear campaign'
- Teen suspect in murder of teacher Colleen Ritzer left 'hate' note, documents say
- Jimmy Breslin, the gravedigger and 'the bleary day' they buried JFK