The frustrated Metcalf was involved in a skirmish with Fred Warner after the 49ers linebacker secured a game-sealing interception off Seahawks quarterback Drew Lock. Cornerback Deommodore Lenoir also got involved, leading to the ejection of both Metcalf and Lenoir.
Pepper's response on social media was, "14 f--ked around and found out." He delivered the message via American Sign Language.
In October, Metcalf revealed that he had started learning American Sign Language.
"I kept getting flagged for my mouthing," the Seahawks receiver told Rich Eisen.
Metcalf first used American Sign Language in a November contest against the Los Angeles Rams, signing "44, my son," after beating cornerback Ahkello Witherspoon for a touchdown.
He did the same against the Dallas Cowboys, signing "standing on business."
After Sunday's loss to the 49ers, when asked if the incident resulted from frustration, Metcalf said, "If you want to call it frustration, yeah, it was frustration. But from my side, he hit me in the back of the head. So I just retaliated from that."
Warner responded more humorously to what sparked the exchange, providing a different account of the events, saying, "Yeah, I don't know what happened, man. I told him he tackles really well, and then, for some reason, he didn't like that. I guess what happened, happened, and it's unfortunate. (He's) got to learn to keep his composure, but happy we came out with the dub."