The incident was ignited after Marlins right-hander Chris Volstad threw behind the Nationals Nyjer Morgan after Justin Maxwell's pinch-hit double.
Morgan spiked his bat and charged Volstad, prompting an all-out series of punching, pushing and grabbing.
Morgan threw a left-handed punch that grazed Volstad's shoulder before Marlins first baseman Gaby Sanchez charged and delivered a blow on Morgan. Both benches and bullpens emptied, and there was plenty of pushing and shoving.
Morgan, who had been struck by a pitch in the fourth inning, and Volstad were ejected, as were Marlins manager Edwin Rodriguez and Florida reliever Jose Veras.
The ejections weren't over. In the seventh inning, Nationals lefty Doug Slaten was ejected after pegging Sanchez with a pitch. Because warnings had been issued, Nationals skipper Jim Riggleman also was tossed.
At the root of the incident was the collision between Morgan and Marlins catcher Brett Hayes in the 10th inning of Tuesday night's game.
On that play, Morgan barreled into Hayes, and the Marlins felt that he would have scored easily had he slid. Instead he was called out, and Hayes sustained a separated left shoulder.
"It was a hard play, and I understand there are going to be some bad feelings," Morgan said. "You've got to get me back. They hit me the first time, and I let it go. But when they throw at me again, I've got to go."
In the first inning on Wednesday, Morgan struck out swinging. He was hit by the pitch in the fourth with the score 14-3.
Morgan took first and proceeded to steal two bases, and he scored on Ian Desmond's sacrifice fly, a play in which Florida second baseman Donnie Murphy dislocated his right wrist.
The Nationals felt that the matter should have been resolved after Morgan was hit in the fourth. But the way Morgan swiped two bags and expressed himself to the crowd, which was booing him, angered the Marlins.
"It gets under everybody's skin, and especially it gets under my skin because there is one way to play this game, and you've got to play with the integrity of the game," Marlins third baseman Wes Helms said. "I cannot stand when a guy shows somebody up, or shows the integrity of the game up to the fans, or whatever. There is no place in baseball for that. In my opinion, you're going to get what's coming to you if you do that.
"Tonight, I think, was the time to show him we weren't going to put up with him, especially after last night. But also, [he was] trying to take the bases when they were down 10 runs. I can't really say anything good about a guy who doesn't play the game right or play for the integrity of the game."
The fact that Morgan opted to steal a couple of bases didn't bother Riggleman, who defended his outfielder.
"My feeling has always been, if you hit somebody, you did what you set out to do," Riggleman said. "If he decides to run on you, that's his business. I have no problem with that at all. We decide when we run. The Florida Marlins don't decide when we run. Nobody decides when we run."
There was plenty of action in the pileup of players, but no one was seriously hurt. Volstad sported a cut and swollen right cheek.
"When I saw [Morgan] running out, obviously, he's not coming out there to talk," Volstad said. "I was just trying to defend myself and not get hurt. Gaby had my back. The whole team had my back. Everyone was there. It's just part of the game."
Bodies were scrambled, with Nationals third-base coach Pat Listach right in the middle. After watching the replay, Volstad was unsure if Listach's helmet caused the lump under his right eye.
"I watched the video. Morgan came across, I think he just scraped me a little bit," Volstad said. "Listach, the third-base coach, I don't know if I got hit with his helmet or something. It's all right, though."
The Marlins went into the game after learning that Hayes' left shoulder was separated during the controversial collision with Morgan on Tuesday night. His arm is in a sling.
Volstad throwing at Morgan was expected, but the right-hander had trouble with his control all night. He'd hit two other batters with pitches before pegging Morgan in the fourth.
Rodriguez said that the game plan was to pitch Morgan inside all series, but the pitch that went behind the center fielder set things off.
"You saw what happened. We've been pitching inside to Morgan all series. We're going to pitch inside," Rodriguez said. "That's the best way to get Morgan out. Volstad went out there. He was trying to pitch him inside, and that's what happened. Then he charged the mound."
Morgan said it was "garbage" that the Marlins took issue with his stolen bases in the fourth inning.
"The game was a little out of whack," he said. "But it's still the fourth inning. If they don't hold me on, I'm going to roll."
Joe Frisaro is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.