Mike Clevinger and his fellow Indians pitchers are making history. (Sean M. Haffey/Getty Images)

BALTIMORE — For a pitcher, a WHIP of 1.000 is a beautiful and mystical number, both aesthetically — with that perfect, indivisible integer on the left and those big, round zeros on the right — and as a delineation of sheer greatness. If your ratio of walks plus hits allowed per inning is a mere one, you are essentially allowing an average of a base runner per inning, and you can safely assume most of them will be harmless.

It is telling that no team has posted a WHIP of less than 1.000 for a full season, and no pitcher in the past 100 years (minimum: 1,000 innings pitched) has been below 1.000 for their career — with the great Mariano Rivera, at 1.0003, coming closest.

But now, consider the 2018 Cleveland Indians. Twenty games into their season, their pitching staff owns a WHIP of 0.977. To translate that in historic terms, every Indians pitcher, collectively, has pitched like 1968 Tom Seaver (0.978), 2011 Clayton Kershaw (0.977) or 1998 Greg Maddux (0.980).

“I definitely pay attention to WHIP,” Indians right-hander Mike Clevinger said. “Keeping hitters from reaching base, obviously, is one of the biggest components in run-prevention. And being under one is really, really good.”

A year ago, the Indians, in going 102-60 and winning the American League Central for a second straight year, possessed one of the best pitching staffs in history. Some advanced metrics, such as WAR (wins above replacement) and ERA- (park- and league-adjusted earned run average), rank that 2017 staff as the best in history.

But if anything, they may be even better this year. Though it is still early, and the Indians have played only seven games against teams currently above .500, their pitching staff has an ERA of 2.57 — second only to Houston’s 2.21 — as well as that dazzling, unprecedented, sub-1.000 WHIP.

“They’re really starting to believe they’re as good as people say,” Indians catcher Yan Gomes said of the team’s pitchers. “Their confidence is growing. It’s something to see.”

In winning three of four from the Baltimore Orioles — to improve to 12-8 on the season, 2 ½ games ahead of the second-place Minnesota Twins — the Indians put on display the sheer virtuosity of their pitching staff, holding the moribund Orioles to seven runs and 21 hits over those four games. All four of their starters in the series — Trevor Bauer, Clevinger, Corey Kluber and Carlos Carrasco — pitched at least seven innings, with Clevinger going the distance in a two-hit shutout. That quartet’s ERA this season: 2.17.

“When these guys are pitching like that,” Clevinger said, “what else can you do besides go out and try to keep up?”

One interesting wrinkle to the Indians’ brilliant pitching thus far: The staff’s collective strikeout rate is down sharply from a year ago, when they set an all-time record with 10.1 strikeouts per nine innings. This year, even as strikeout rates continue to climb across the game, the Indians’ rate is down to 8.2 per nine innings, which ranks just 22nd in the majors.

It is a drop-off the Indians attribute to a change in the way hitters are approaching them. Perhaps cognizant of the Indians’ strikeout propensity — and their arsenal of filthy “out” pitches — opposing hitters appear to be trying to jump on pitches early in the count, rather than falling behind and getting set up for a nasty, two-strike offering.

“They know we’re going to throw strikes, and they know we have good stuff,” said Kluber, a two-time Cy Young Award winner. “So they’re going to be aggressive against us. But if we execute pitches, we’re going to get quick outs, and if you do that, you have a chance to pitch deep in the game. If you can have two or three 10-pitch innings, it’s almost like gaining an extra inning.”

In an era when starters’ share of innings pitched is dropping to historically low levels — barely above 5 1/3 innings, on average, in 2018 — Indians starters are averaging 6 2/3 innings per start.

“If we are getting early outs, I’m a big fan of that,” Manager Terry Francona said Monday. “There’s something to be said for missing bats, but there’s also something to be said for getting a six- or seven- or eight-pitch inning. It lets those guys go a little deeper. There’s usually an inning or two, even when the guys have good games, where it’s a pretty lengthy inning and they have to reach for a little more, so it’s nice to have those innings where you maybe get some early contact.”

The mastery of the Indians’ pitching staff has masked a sluggish offense in the season’s first few weeks. Through Monday, Indians hitters ranked 27th in the majors in OPS (.646), 30th in batting average (.215) and 25th in runs per game (3.5). Already this season, they have managed to lose three games when they held opponents to two or fewer runs. Some of their most accomplished hitters have yet to approach their normal production, from Edwin Encarnacion (.149/.241/.324) to Jason Kipnis (.173/.247/.222) to Francisco Lindor (.224/.290/.353).

“We understand we’re going to go through stretches like this,” Lindor said Monday. “If it happens in June or July, and you’re hitting .280, .290, .300, nobody notices too much. But now, everybody’s like, ‘Wow, they’re hitting like that?’ But I have 750 [plate appearances] left. I would like for us to come around as hitters, but I know we will. It’s just a matter of time.”

And when that happens — when the Indians’ hitters begin producing the way their track records say they should — the Indians’ pitchers will welcome the support. But as they have shown through some four weeks of early-season brilliance, they hardly need it.

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