The 2008 World Series MVP was suspended for intentionally throwing at the Washington rookie in the Philadelphia Phillies' 9-3 win over the Nationals on Sunday night.
Major League Baseball announced the penalty Monday. Hamels also was fined.
Hamels wasn't available to reporters before the Phillies opened a three-game series against the New York Mets. But he already admitted that he deliberately threw at Harper.
"I was trying to hit him," the two-time all-star lefty said Sunday night. "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."
Hamels began serving his suspension Monday night. With Cliff Lee expected to come off the disabled list and start Wednesday, coupled with Thursday's day off, Hamels really won't miss a turn in the rotation.
Roy Halladay will likely pitch on regular rest Saturday and Hamels would then start Sunday against the San Diego Padres.
Phillies general manager Ruben Amaro Jr. was disappointed the incident occurred.
"Obviously that's not what we're about," Amaro said. "We're not about trying to injure people. Things that happen in the game happen in the game. Those are parts of the game. But as far as how the Phillies want to conduct themselves, we try to take the high road on things. By no means are we condoning this. We fully support what the commissioner's office has decided to do."
Hamels plunked Harper in the small of the back with a fastball in the first inning. He said the purpose pitch was his old-school way of welcoming the 19-year-old Nationals phenom to the big leagues.
"That's something I grew up watching, that's kind of what happened. So I'm just trying to continue the old baseball because I think some people are kind of getting away from it," Hamels said. "I remember when I was a rookie the strike zone was really, really small and you didn't say anything because that's the way baseball is.
"But I think unfortunately the league's protecting certain players and making it not that old-school, prestigious way of baseball," Hamels added.
Harper got the last word, though. When Hamels made a pickoff to first, Harper stole home for the first swipe of his eight-game big league career.
In the third inning, Nationals starter Jordan Zimmermann hit Hamels in the left leg with one out and a runner on first when the Phillies pitcher squared to bunt. Home plate umpire Andy Fletcher warned both dugouts.
Nationals general manager Mike Rizzo told The Washington Post that Hamels hitting Harper with a pitch was "classless" and "gutless."
According to the newspaper's website, Rizzo also said: "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."
Phillies manager Charlie Manuel said he wished Hamels wouldn't have been so forthcoming with his comments.
"He could have been a little more discreet or less honest," Manuel said. "The way I look at it, baseball is going to take care of it between the two teams on the field. To me, that's the issue. When they hit Cole, it set it even. At the same time, the best way to handle the Nationals is to beat them on the field."
As for Rizzo's reaction, Manuel brushed it off.
"I think that if we beat them on the field, that will take care of our business and that takes care of it," Manuel said. "When they hit Hamels, that takes care of it and we're back on even ground. There was no warning or nothing. They had a chance to get even. That even made it a wash. What Rizzo says is no concerns to me."