To challenge the ruling on the field, i.e. call someone out on something that you believe is bullshit.
Derived from the NFL practice of coaches throwing a red flag to request further review of a play and give the network a chance to show 2 more minutes of commercials.
person 1 - My bad on not helping you out, I was working all day yesterday...
person 2 - I'll throw a red flag on that, you told me three days ago that you don't work weekends...
One of the great American hockey teams with 11 cups under their belt and 20 strait playoff runs, this is a prestigious team. Mostly hated due to butthurt newfriends, who are mad because their Chicago Blackhawks got beat by the Red Wings again, or because the Red Wings are at the top of the Central-Division and their team isn't.