Just as drinking is associated with St. Patrick's Day, it's also associated with fighting.
When drunk people gather, fights are bound to happen—especially on St. Patrick's Day. Things got particularly vicious outside of this McDonald's on West 3rd Street in New York. This place has a history of violence, and the excessive liquor sure didn't help.
Make sure you watch the entire fight, because things heat up again just when you think it's all over.