Washington Nationals General Manager Mike Rizzo is so old school, he would have been just fine studying in the one-room type. You almost expect Rizzo to be photographed only in black and white.

He’s a baseball lifer who believes in playing hard and keeping your mouth shut about what happens on the field. So the surprising admission of Philadelphia Phillies starter Cole Hamels, who revealed he drilled Bryce Harper on purpose in Sunday’s game, was like issuing a bench-clearing challenge to Rizzo’s sensibilities. He considered Hamels’s “I-was-trying-to-hit-him” candor a knockdown pitch to baseball etiquette. For Rizzo, the only appropriate response was to, in effect, charge the mound.

While blasting the pitcher Monday for his “classless, gutless . . . act” in a phone conversation with Post reporter Adam Kilgore, Rizzo urged Major League Baseball Commissioner Bud Selig to suspend Hamels. (Selig obliged: Hamels was suspended for five games. On Tuesday, MLB fined Rizzo an undisclosed amount for his public comments.)

As a starter, Hamels usually pitches only once every five days, anyway. With Philadelphia off Thursday, the left-hander began serving his suspension immediately.

The Phillies could easily align their rotation so that Hamels does not miss a start. Selig, though, did hit Hamels in the wallet: He stands to lose about $400,000 of his $9.5 million salary.

Let’s be clear: Hamels wasn’t head-hunting. With his pinpoint control, he probably hit Harper where he intended, give or take a few inches. But what if Hamels’s 93-mph fastball had gotten away from him? And then Hamels broke with protocol in providing on-the-record commentary?

For all of that, Rizzo’s passionate comeback was on point. In delivering a fiery defense of the future (current?) face of the franchise, Rizzo reinforced the growing belief in baseball that the Nationals are no longer pushovers.

Rizzo’s move did more than simply fuel an intensifying regional rivalry between National League East opponents. Whether he intended to or not, Rizzo launched a warning shot to the entire league: The new-look Nationals might not start the fight — but they’ll gladly finish it.

By the time I caught up with Rizzo on the phone Monday, I figured he had cooled down. My bad.

“He tried to pound his chest on the back of Bryce Harper,” Rizzo said of Hamels. “He popped off trying to be a tough guy. Yeah, well, I’m not gonna have it. Not with my player. No way.”

Pitchers have thrown at batters since the days of horse-drawn buggies and handlebar mustaches. So-called “purpose pitches” are as much a part of baseball as chalk.

They’re the game’s most direct form of communication: When pitchers (or entire teams) are trying to send a message, someone gets plunked.

Harper, 19, is baseball’s highest-profile rookie. Harper’s picture was on magazine covers long before he became a multimillionaire after signing with the Nationals at 17. Last year in the minors, Harper angered old-school types by blowing a kiss in the direction of a pitcher after smashing a home run against him.

He has talked about having a bright-lights city life similar to that of former iconic quarterback Joe Namath, who was once the prince of New York City. A bull’s-eye patch might as well have been stitched on Harper’s Nationals jersey even before his Hollywood-worthy big-league debut.

Bottom line: Harper was bound to be on the receiving end of some statement pitch from someone. Hamels’s mistake was being so frank about his intentions.

In a different era, Hall of Famers such as Don Drysdale and Bob Gibson intimidated through knockdown pitches. Former Dodgers great Maury Wills once told me that when you stepped into the batter’s box against Gibson, you had better be prepared for a pitch anywhere. “And anywhere,” Wills said, “usually meant right at your head.” In an era of multi-million-dollar salaries, the threats of injuries and unpaid suspensions has decreased the frequency of “beanball” wars.

On Sunday night, the Nationals policed the situation correctly. Harper went to first base without incident and later stole home. Washington starter Jordan Zimmermann hit Hamels and maintained his innocence. Everything probably would have ended there if Hamels had zipped it.

“I know all about guys getting hit, sending messages and all that stuff,” Rizzo said. “I’ve been in this game 30 years. I’m an old-school guy. But hitting a 19-year-old rookie and then going out there and talking about it. . . . That’s not the way you do it. That’s not going to make us [back down].”

For its part, Phillies management also would have preferred for Hamels to be less forthcoming. Why give the Nationals bulletin-board material and hand Selig a signed confession?

Still, some would argue that Rizzo took his criticism of Hamels too far. Is Rizzo writing checks with his mouth the Nationals players will have to cash on the field? Absolutely. And I’m good with that.

As the head of Washington’s baseball operations, Rizzo must establish an organizational culture. Among the District’s professional sports teams the past two decades, most have been weak.

Under Rizzo, the Nationals will stand up for themselves on and off the field. So go ahead and bring it.

“I’ve never had anything bad to say about the Philadelphia Phillies,” Rizzo said. “They’re a well-run organization. They’re the king of the mountain . . . but what [Hamels] did was wrong. We’re trying to knock off the king of the mountain and become the kings . . . and I’m going to say it like it is.”

Rizzo knows no other way. If anyone in baseball didn’t know that before this episode, they sure do now.

For Jason Reid’s previous columns, go to washingtonpost.com/reid.