Hamels struck the Washington rookie phenom in the small of his back with a 93-mph fastball in the first inning of Philadelphia's 9-3 victory, then admitted that the move had been intentional.
Hamels on Monday received a five-game suspension from Major League Baseball, along with an undisclosed fine.
"I was trying to hit him," Hamels said after holding the Nats to one run in eight innings. "I'm not going to deny it. I'm not trying to injure the guy. They're probably not going to like me for it, but I'm not going to say I wasn't trying to do it. I think they understood the message, and they threw it right back. That's the way, and I respect it. They can say whatever they want."
Rizzo responded Monday morning, telling the Post's Adam Kilgore: "I've never seen a more classless, gutless [expletive] 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."
A rivalry has begun to take shape between the surprising first-place Nationals and the five-time defending National League East champion Phillies after Washington took two of three over the weekend.
After Harper was hit by the pitch, he took first base without any disruption. He later stole home when Hamels attempted a pickoff throw to first base. Nationals starter Jordan Zimmermann then hit Hamels with a pitch in the third inning, which resulted in a warning for both benches.
Zimmermann said afterward he had no intention of hitting Hamels.
"I wish [Hamels had] been a little bit more, what do you call it, not so honest, or dishonest, or discreet, that might be the right word," Phillies manager Charlie Manuel said on Monday on 94.1/610 WIP. "What I saw was the next time Hamels came up to bat, they definitely retaliated, he got hit on the calf and he could have got hurt. If the guy would have hit him hard on the bone part of his leg, that could have hurt. ... I like to think it was dropped right there and the rest of it will be done baseball-wise."
According to the Post, the league is reviewing the incident on Monday and a suspension could be handed down since Hamels admitted the hit-by-pitch was intentional.
"This goes beyond rivalry and all that stuff," Rizzo told the Post. "This points to, you take the youngest guy in baseball. He's never done a thing. And then Hamels patted himself on the back. Harper's old school. Hitting him on the back, that ain't old school. That's [expletive]."