The Pittsburgh Pirates likely will host the Chicago Cubs in the NL Wild Card Game — but will have to face ace Jake Arrieta

To think, there used to be real conversations about whether the Cubs should start Jon Lester or Jake Arrieta in a potential Wild Card Game. I don’t want to shortchange Lester, who’s a terrific pitcher in his own right — one of the better pitchers in the National League. But Arrieta is just on one of those runs. If you want to play along and say something stupid like "Arrieta’s on a run that he’s earned," then that would be exactly three fewer earned runs than Arrieta has allowed since the beginning of August. Roll your eyes all you want, but don’t pretend like that sentence wasn’t effective.

There’s a certain detectable sense of dread. The Pirates and Cubs are guaranteed a one-game playoff to determine who advances to the NLDS. The only question is where it’ll be played, but the odds-on favorite at the moment is Pittsburgh. People have complaints about the one-game-playoff format. Some of them are legitimate, even given that playoff series don’t do much better to crown the deserving ballclub. But this is what we have, and it’s exciting, and it just means the Pirates get the misfortune of facing Arrieta with everything on the line. He’s an opponent who feels unbeatable. I don’t want to take anything away from Gerrit Cole, but it feels like it’s lopsided. There’s no one in the game pitching better than Arrieta has.

Arrieta just faced the Pirates, in Chicago. He got himself pretty deep into a perfect game. A week and a half earlier against the Pirates, Arrieta gave up two runs (one earned) in eight innings. In early August, he blanked the Pirates over seven frames. In the middle of May, he gave up one run in seven innings. Toward the end of April, another one-run, seven-inning outing. It’s not like the Pirates haven’t had chances. Arrieta has just been that dominant. The Cubs have lost just one of his past 17 starts; in that game, they got no-hit. Arrieta is officially an adversary you worry about.

The attention is on the Pirates. It’s on how they intend to win this seemingly unwinnable game. Buster Olney just talked to some people in the industry about what the Pirates are supposed to do. The general message is that the Pirates are up against it. There’s nothing as psychologically daunting as an ace, and Pirates fans can just think back to last October’s one-game playoff, against Madison Bumgarner. He never seemed to even give them an opportunity to advance. It’s true: Arrieta could well take over the game. He could literally win it on his own, like he did the other day, with seven shutout innings and a homer. But history, at least, isn’t quite so pessimistic. The Pirates’ odds aren’t as long as they seem.

You’re familiar with OPS, and you might be familiar with OPS+. OPS+ basically just compares OPS to the average. A mark over 100 means better hitting than usual. A mark under 100 means worse hitting than usual. I want to take a quick look at OPS+ allowed. This year, Arrieta has allowed an OPS+ of 45. That ties him with Zack Greinke, and it’s also spectacularly good. Clayton Kershaw, if you’re curious, is at 50. Last year, Arrieta finished at 53. He’s been phenomenal for consecutive seasons. He’s been even more effective the last few months, but bigger-picture stats tend to be more predictive than smaller-picture stats. We have two years now of Arrieta conceding a combined OPS+ around 50. He’s been arguably the best pitcher in the game.

Intrigued by this, I chose to investigate the playoff history of such standout performers. Using the Baseball-Reference Play Index, I went back to 1961 and found all the qualified starting pitchers who, during the season, allowed an OPS+ no higher than 50. Then I looked up which of those pitchers pitched in the subsequent playoffs. I wanted to know how their teams did. This is a small group, but it has names like Randy Johnson, Roger Clemens and Greg Maddux. Those outstanding pitchers went on to start 35 games in the playoffs, excluding a Justin Verlander start that had a long early rain delay. Their teams ultimately won 63% of the time.

An advantage, for sure. Loosening the restriction to an OPS+ of 55 instead of 50, then you get 75 games, with a winning percentage of 60%. And if you loosen further to an OPS+ of 60 instead of 55, then you get 104 games, with a winning percentage of 55%. Some pitchers included with this last loosened restriction are Max Scherzer (2013) and Greg Maddux (1996). These are still unquestioned aces. David Price this year has allowed an OPS+ of 72.

The simple takeaway: The ace starters have helped their teams win more than they’ve lost, but the games certainly haven’t been unwinnable for the opponents. Figure, with a guy around Arrieta’s level, the winning percentage is in the vicinity of 60%, meaning, for the opponents, it’s about 40%. Another way of imagining 40%: Andrew McCutchen has an OBP of .405. So just based on this, the Pirates’ odds are roughly like McCutchen’s odds of reaching base in a given at-bat.

It doesn’t necessarily have to be about solving Arrieta. That is one option. But Cole could just match Arrieta frame for frame. On May 17, when Arrieta allowed one run to the Pirates in seven innings, the Cubs lost 3-0, because A.J. Burnett went seven scoreless. So Cole could be great, or the Pirates could benefit from good old-fashioned luck. I’ve seen a baseball game end with a walk-off balk. I’ve seen a baseball game end with a walk-off strikeout. Close games can be decided by anything. The Pirates just have to stay close.

You don’t have to think that hard to find cases of a team in the playoffs beating an ace. Clayton Kershaw has pitched around Arrieta’s current level for three years in a row. And yet the Dodgers have lost four straight playoff Kershaw starts, all to the Cardinals. Michael Wacha started two of those games. Adam Wainwright one, Shelby Miller the other. It’s not really possible to be better than Kershaw has been. Yet we’ve seen what’s happened. It’s been enough to give Kershaw a little bit of a reputation.

Take the season numbers at face value, and the average Gerrit Cole start has 2.2 runs in 6.5 innings. The average Arrieta start has 1.6 runs in 7 innings. Arrieta is better. In each start, he’s better by the bulk of one run. But there’s one more thing the Pirates should have going for them. It’s not set in stone, but it would be a surprise if the Pirates don’t have home-field advantage.

The Pirates are 51-27 at home. That’s really good. The Cubs are 45-33 on the road. That’s also good. We know there exists such a thing as home-field advantage, and while the Pirates aren’t that good at home, history shows us that, in the playoffs, the home team has won 55% of the time. It can be a difficult advantage to notice because it doesn’t always manifest clearly, but it’s there, and we have to believe it’s always there. And the thing about it is that the Pirates’ advantage because of playing at home eats away at the Cubs’ advantage because of starting Arrieta.

This is all pretty mathy, and I don’t want to pretend like math can predict what’s going to happen in one specific game. The last ace the Pirates faced in a one-game playoff shut them down. The previous ace the Pirates faced in a one-game playoff collapsed under the pressure. Those are opposite sides of the spectrum, and Arrieta could end up anywhere in there. Maybe he will take the game over. But the Pirates really do have a decent shot. They might be underdogs, but despite the Arrieta menace, I’d probably put their odds of winning around 40% to 45%. The Cubs will be favored, but it’s almost close enough to be a coin flip, so it’s not really so bad. Are the Pirates surprised when McCutchen reaches base? That’s a better representation of what the team is up against.