Find the fattest, reddest marker you can and circle May 21, the day of the Washington Nationals’ next game against the Philadelphia Phillies. In the hours after the final out of the teams’ three-game series at Nationals Park this past weekend, the rhetoric between the two clubs only intensified.

The Nationals had marketed the series as an appeal to Washington fans to “take back the park” from Philadelphia followers, who regularly made the two-hour trek to support their team. Sunday night, it became clear the enmity between the sides has extended to the players and executives as well.

Phillies pitcher Cole Hamels admitted after the game he had drilled Nationals 19-year-old rookie Bryce Harper with a pitch on purpose. Monday morning, Washington General Manager Mike Rizzo blasted Hamels, calling the move “classless” and “gutless” while labeling Hamels “fake tough.” Rizzo called on Major League Baseball to suspend Hamels, and by Monday evening, the pitcher had been handed a five-game ban.

Meanwhile, former Phillie Jayson Werth said he could hear Phillies fans taunting him as he walked off the field Sunday night with a broken left wrist, suffered after he slid to catch a fly ball. Werth underwent surgery Monday at the Mayo Clinic in Rochester, Minn., performed by Richard Berger, to repair a distal radius fracture. He will miss roughly 10 to 12 weeks.

In an e-mail to the Post, Werth, a member of the 2008 World Series champion Phillies, vowed he would return, motivated to keep Phillies fans from ever seeing another title parade.

“After walking off the field feeling nauseous knowing my wrist was broke and hearing Philly fans yelling ‘You deserve it,’ and, ‘That’s what you get,’ I am motivated to get back quickly and see to it personally those people never walk down Broad Street in celebration again,” Werth wrote.

Hamels said after Sunday’s game he had drilled Harper in his first at-bat as a nod to “that old-school, prestigious way of baseball.” Rizzo took exception and responded in harsh and explicit terms.

“Players take care of themselves,” Rizzo said in a phone conversation that was laced with expletives. “I’ve never seen a more classless, gutless . . . act in my 30 years in baseball.

“Cole Hamels says he’s old school? He’s the polar opposite of old school. He’s fake tough. He thinks he’s going to intimidate us after hitting our 19-year-old rookie who’s eight games into the big leagues? He doesn’t know who he’s dealing with.”

Rizzo said player safety should take precedence and Hamels should miss at least one start. Later, the league’s five-game suspension ensured Hamels would suffer financially. But the Phillies, because of an off day Thursday, can manipulate their rotation to ensure Hamels will not miss a start.

“With all the bounty [stuff] going on in professional football, the commissioner better act with a purpose on this thing,” Rizzo said. “Players have a way of monitoring themselves. We’re not here to hit people and hurt people.

“He thinks he’s sending a message to us of being a tough guy. He’s sending the polar opposite message. He says he’s being honest; well, I’m being honest. . . . That was a fake-tough act. No one has ever accused Cole Hamels of being old school.”

After getting hit, Harper placed the bat down and walked to first base. Two batters later, acting on a pregame lesson from Werth and third base coach Bo Porter, he stole home.

“I knew how he was going to respond,” Rizzo said. “I’m sure he won’t be happy that I’m sticking up for him.”

In Philadelphia, Phillies General Manager Ruben Amaro Jr. did not respond to Rizzo’s remarks, but said he was disappointed in Hamels’s decision to hit Harper.

“As far as how the Phillies are going to conduct ourselves, we like to try and take the high roads on these types of things,” Amaro said. “By no means are we condoning trying to endanger another player.”

Phillies Manager Charlie Manuel, 68, recalled how getting hit by an opposing pitcher was part of the game when he played. “That’s what old-school baseball was about,” Manuel said before Monday’s Phillies game against the visiting New York Mets. “But evidently, we definitely don’t play that way no more.”

Rizzo, the longtime scout who turned the Nationals into a contender largely through bountiful drafts, has revealed the fiery part of his personality in the past when backing a player. Last year, he became the first general manager fined by MLB for yelling at an umpire.

“If Cole Hamels wants a dogfight, he met a junkyard dog in Mike Rizzo,” said Harolyn Cardozo, Rizzo’s special assistant and longtime confidante.

When told Hamels admitted to hitting him on purpose, Harper said he had “no clue” why. “He’s a great guy, great pitcher, knows how to pitch,” Harper said. “He’s an all-star. It’s all good.”

Nationals starter Jordan Zimmermann later hit Hamels as he squared to bunt, but he maintained his innocence after the game and received no discipline from the league.

“He was bunting, and I’m going to take an out when I can get an out,” Zimmermann said. “I was trying to go away, and I cut a fastball really, really bad and hit him in the knee.”

Hamels, a 28-year-old left-hander, allowed one run over eight innings Sunday night in the Nationals’ 9-3 loss. He is eligible for free agency after this season and likely will command one of the richest contracts ever for a pitcher.

Correspondent Matt Breen in Philadelphia contributed to this report.