The movie is based on the real life story of friends that play, of course, tag:
The game they play is fundamentally the same as the schoolyard version: One player is “It” until he tags someone else. But men in their 40s can’t easily chase each other around the playground, at least not without making people nervous, so this tag has a twist. There are no geographic restrictions and the game is live for the entire month of February. The last guy tagged stays “It” for the year.