Arenado dodged an inside fastball on the first pitch of the bottom of the third, then ran to the mound swinging at Perdomo, who avoided the jabs and tossed his glove in defense. Both clubs then stormed the field, mostly attempting to break up the fracas.
"I didn't like it. They thought they had to do something, but I had to do something too. That's kind of why I went out there," Arenado said.
Many from both clubs indicated the fracas resulted from a sequence of three hit batsmen the past two games, including one to Manuel Margot that sent him to the disabled list with bruised ribs. Earlier in Wednesday's game, Rockies shortstop Trevor Story was hit by a two-seam fastball in a 1-1 count in the first, and Padres right fielder Hunter Renfroe was hit on the hand with an 0-1 two-seamer in the second. Both were with two outs.
"They're clearly pitching aggressively inside," Padres manager Andy Green said. "[Scott] Oberg has hit two of our guys. [German] Marquez drilled Hunter today, so they're pitching aggressively inside. We've seen that repetitively. Our guys at some point in time are going to take up for each other, and we're going to pitch inside as well."
After the inside pitch, Arenado burst from the batter's box and wielded his right fist at Perdomo, who narrowly avoided a clean punch to the face, instead getting clipped in the back of the head. Rockies left fielder Gerardo Parra landed a punch on Padres catcher A.J. Ellis, and Rockies starter Marquez was seen throwing his fists.
Arenado, Parra, Perdomo, Ellis and Marquez were the only players ejected.
"I don't know how long -- hopefully it's not a long time -- but I expect something to be happening," Arenado said of the potential for a suspension.
The Padres had been pitching Arenado low and away the entire series, so when Perdomo threw toward Arenado's back, the Rockies' third baseman immediately charged.
Crew chief Brian Gorman said Perdomo was ejected for intentionally throwing at Arenado, though Perdomo declined any intention, saying the pitch "got away from me." Ellis was ejected for retaliating, per Gorman.
"Our job is to try and calm everything down, but you've got to eject the aggressors," Gorman said.
Added Ellis: "They just said I was part of instigating, but I think I was just out there doing what we were all doing. That's having each other's back and protecting each other."
Arenado was still steaming after the scuffle had subsided, with Rockies right fielder Carlos Gonzalez restraining him toward the dugout. Padres first baseman Eric Hosmer, a teammate of Arenado's from last year's World Baseball Classic, also approached Arenado without aggression, as did Padres bench coach Mark McGwire.
"My one concern was trying to protect Nolan," Gonzalez said. "I grabbed him and tried to push him toward home plate. Then [McGwire] approached him. There were some back-and-forth words, and it was pretty much the game thing. He was like, 'You hit a couple of our guys, what do you expect?'"
Oberg texted Margot after Tuesday's game and said Margot -- who was in such pain he didn't even attempt to take first base -- had acknowledged his apology positively. Oberg also said Hosmer approached him after the scuffle died down indicating Oberg wasn't the direct cause of the retaliation, but that the incident on Tuesday played a part.
"I think it just shows we have each other's backs," Hosmer said. "I think that's the main thing. You want to fight with your guys, especially coming on the road to a division opponent. You want to stick together."
"They've been pitching aggressively, and we've had some guys that have been hit," Ellis said.
"We had a guy sent to the hospital last night. Two guys get hit on their hands in the past week against these guys. But to react like that and go out there, especially when he didn't even get hit and the ball was behind him, you go out there and make sure everybody's safe and you take care of your teammates."
Gorman said warnings weren't issued until after the scuffle because there wasn't clear intention on the other hit batters.
Immediately after the fracas, the Rockies surged to a five-run frame to take a 5-0 lead en route to their sixth win in 13 games this year. These clubs have met seven times already this season, and have another three-game series at Coors Field in two weeks. Irritation was still high in the immediate aftermath, particularly given the competitive environment of two clubs who see each other 19 times within the National League West.
"You expect anything," Hosmer said. "Especially when you play guys in the division. We're all competitors and we're all trying to do everything we can to win ballgames and compete out there. There's a reason all these guys are at the top level, because of their competitiveness."
"We'll see," Arenado added. "I don't have the answers for that one."