Richard Sherman's beef with San Francisco 49ers wide receiver Michael Crabtree stems from a handshake snub during the 2013 offseason.
According to Sherman's brother who was speaking to the Seattle Times, the mutual hatred started after the Seahawks corner tried to shake Crabtree's hand at Larry Fitzgerald's charity event last summer.
Crabtree allegedly rejected his offer and tried to start a fight with the All-Pro cornerback.
Of course, how much of this is actually true is open to debate - it is the testimony of Sherman's brother after all.
What isn't is the fact the Sherman treated us to one of the most entertaining post-game interviews in NFL playoff history after his Seahawks beat the 49ers 23-17 on Sunday night.
He pulled off the game-winning play, tipping a Colin Kaepernick path destined for Crabtree back into the path of linebacker Malcolm Smith for an interception with just 22 seconds remaining.
And he then mocked the 49ers receiver in his interview with Fox Sports sideline reporter Erin Andrews, barking about how he's the "best in the game".
And to be fair to him, he probably is.
As for what Sherman had to say about the incident, he appeared to confirm his brother's account.
Writing in his column for mmqb.com, Sherman said: "It goes back to something he said to me this offseason in Arizona, but you’d have to ask him about that.
"A lot of what I said to [Erin] Andrews was adrenaline talking, and some of that was Crabtree. I just don’t like him."
As for as the narrative about how the beef started, we'll let you decide who to believe...