The Washington Nationals' disappointing season took a dramatic turn for the worse in the eighth inning of Sunday's game.
Replays appeared to show Papelbon taking issue with Harper not running out the fly ball, at which point the two engaged in heated words and had to be restrained by teammates.
The Nationals were locked in a 4-4 tie with Papelbon's former team, the Philadelphia Phillies, when the incident occurred.
A reverse angle clearly shows Papelbon placing his hands near Harper's throat and slamming the 22-year-old slugger into the back of the dugout.
Harper was pulled from the game following the brief brawl, while Papelbon re-entered the contest in the ninth and allowed a go-ahead, two-run homer to Phillies third baseman Andres Blanco. The All-Star reliever was pulled after allowing five runs - two earned - on one hit and two walks.
"First of all, let me say I'm in the wrong here," Papelbon said postgame. "I've talked to Bryce and told him how I feel. We're on the same page now, which is good, and squash this and head to tomorrow's game."
Harper later acknowledged the conversation with Papelbon, and is also ready to move past the incident.
"He apologized, so whatever," Harper exclaimed. "I really don't care. ... It's like brothers fighting. That's what happens. I'm looking forward to the next six games."
The Nationals entered the year as World Series favorites but were unceremoniously eliminated from playoff contention on Saturday - a week before the season ends - when the New York Mets clinched the NL East title.