According to the OED, they have very recently changed the definition of the phrase...Beating a Dead Horse.

They now define that phrase...Beating a Dead Horse to mean:

"A beating of the Denver Broncos professional football team by the Seattle Seahawks professional football team, by a score of more than 30+ points, in a game titled as the SuperBowl, to such a degree that the national media has dubbed this a blowout by one team over the other. When the Denver Broncos, a team representing the AFC as the best that this league has to offer, is beaten so badly by the opposing force...i.e., the Seattle Seahawks, a team representing the best that the NFC has to offer, this constitutes a change in the definition of the phrase, and shall henceforth be used as an example of the phrase...Beating a Dead Horse. "


BTW, just for edification, the OED offered this little tidbit of a scenario of a group of Seahawks eating away at a downed Bronco

For those that don't believe in watching a SuperBowl that you do not have a horse in that race (pun intended), the final score was....

Seattle Seahawks 43......and the Denver Broncos 8