The Post's Jonathan Forsythe talks with Nationals beat writer Adam Kilgore about why the Nationals have struggled this season. (The Washington Post)

In baseball, sometimes only the numbers can do the speaking. Entering Tuesday night, when Wilson Ramos catches, the Washington Nationals’ ERA this season is 3.30. When Kurt Suzuki catches, the Nats’ ERA is 3.96, two-thirds of a run higher.

Such a difference is astronomical. It’s far too great a gap to have much to do with stopping base stealers or blocking pitches in the dirt. It can only center on one mysterious, vital and almost completely unstudied area of baseball: pitch selection, also known as “calling a game.”

To give a sense of magnitude, a hypothetical team with catchers who helped a staff lower its ERA by 0.66 would save about 108 runs. That’s worth about a dozen extra wins or the difference between being a .500 team and making the playoffs.

What catchers have such huge influence? Buster Posey’s catcher ERA is 3.79. His backup in San Francisco is 4.77. The Dodgers’ A.J. Ellis is 3.08. L.A.’s other backstops have respective ERAs of 3.67 and 3.77. Miami backup Jeff Mathis may be the best; he has improved three different staffs significantly in the last three years but seldom plays; he’s a .197 career hitter. Most teams show little difference among their catchers, but those who do have a huge advantage.

Perhaps the biggest factor in how much the Nats bounce back the rest of this season and next is whether the often-injured Ramos can start at least 75-80 percent of their games.

The Post Sports Live crew debates whether Mike Rizzo deserved a promotion from Nationals general manager to president of baseball operations. (The Washington Post)

Before you say, “Maybe it’s a fluke,” look at the career ERAs of every current Nats starter except for Ross Ohlendorf, who has made only two spot starts for Washington. In nearly every case, Ramos is better by a gap that ranges from significant to huge:

Stephen Strasburg, 2.72 in 20 starts with Ramos vs. 3.27 in 13 Suzuki starts;

Gio Gonzalez, 2.54 in 13 Ramos starts vs. 3.66 in 101 starts with Suzuki (many in Oakland);

Ross Detwiler, 3.00 in 105 innings with Ramos vs. 4.24 in 1101 / 3 innings with Suzuki;

Taylor Jordan is 3.22 vs. 4.70 in limited starts with each;

Dan Haren is the most stark: a 2.81 ERA in 11 Ramos games and 5.05 in 25 Suzuki starts, including some in Oakland when Haren was younger and better.

Only Jordan Zimmermann has done slightly better with Suzuki, 3.50 to 3.54.

In the Nats’ bullpen this year, Rafael Soriano has pitched to Suzuki 28 times with a 4.28 ERA and to Ramos 21 times with a 3.43 ERA. In their careers, Tyler Clippard, Drew Storen, Craig Stammen and Ryan Mattheus all have lower ERAs with Ramos, Mattheus by almost two full runs.

Why? “Ramos will pitch inside more,” Manager Davey Johnson said. “I like the way Ramos sets his target better than Suzuki,” who sets his mitt very low.

Beyond that: silence. Baseball is the chatty game. You can ask anything, except, “How do you pitch to that guy?” That’s the central secret.

Pitch-calling is such a dark art that your only rational recourse is to see which catcher wins most often. For now, that’s Ramos. Why? What’s the origin of his success? Will it continue? He has played just 204 games.

“I followed Ivan Rodriguez’s career when I was young,” Ramos said in an interview in a Nats in-house publication. “Getting an opportunity to play with him here [in late 2010 and all of ’11] was unbelievable. . . . I think calling the game is the most important thing for the catcher.”

Some catchers, such as Hall of Famer Gary Carter, literally keep a little black book of daily info on every pitcher and hitter they face. Some, like Suzuki, are known for exhaustive film study. Some start with a game plan but rely heavily on “reading the bat,” sensing the hitter’s intentions by his reaction to the previous pitch. Some just “feel the game” and their pitcher.

The difference in performance can border on unbelievable. Strasburg has 33 walks and 76 strikeouts pitching to Suzuki but a dazzling 21-120 ratio with Ramos. In his career, Detwiler has pitched almost an identical number of innings to each. But Detwiler has allowed 48 extra-base hits with Suzuki and just 22 with Ramos.

At the least, the Nats and Suzuki need to study Ramos — or debrief him — to find out his ideas because he’s getting much more out of the same staff.

Ex-Nats Manager Jim Riggleman said he once sat in the stands with a famous general manager, a successful manager and two well-known scouts, and they analyzed what the next pitch would or should be for a whole game.

“We almost never agreed on any pitch call,” Riggleman said.

If a starting pitcher has four different pitches and can aim at any of four quadrants of the plate, there are just too many permutations to have any rules. And there are probably a dozen “locations” that pitchers aim at, not just the four big quadrants. The lesson Riggleman took: There is no “right pitch” to call, but sometimes there is a “wrong pitch.”

Analyzing catcher ERAs can lead you astray because there are so many variables. For example, Tim McCarver had respective catcher ERAs of 2.44 and 2.82 with Bob Gibson and Steve Carlton in 450 of their starts. Their ERAs were 3.26 and 3.41, respectively, with all their other catchers. Did McCarver just get to work with them in their primes? How much really was his impact?

What makes Ramos fascinating is that he has worked with all the Nats pitchers at random and in a three-year time frame. Even if we can’t know every subtle factor, it looks like he improves almost everybody. He has had healthy seasons of 126, 113 and 113 games, including the minors.

Students of advanced metrics correctly search for players who might improve a team’s run differential by 20 runs in a year. That might add two extra wins — a bonanza. But what if you found a catcher whose pitch calling, defense, presence — whatever it is — could save a-third-of-a-run or, like Posey, perhaps even half-a-run in 125 games a year? That’s worth five-to-seven extra wins a year before you include any value as a hitter.

Is Ramos such a catcher? In the past two years, his catcher’s ERA is 3.23. All other Nats catchers have a combined ERA of 3.58. It’s possible.

You can make a case that McCarver, over 21 seasons, proved he added real extra value. For the 26-year-old Nats catcher, the verdict is not yet in. But when it arrives, a healthy Ramos could be one of the most powerful pieces of the Nationals’ future.

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