The Cubs’ Starting Rotation is Historically Good

It’s been said enough by now, that you won’t be surprised to hear that the Chicago Cubs pitching staff – particularly the starting rotation – is the very best in baseball.

But just how good are we talking about here? Just the best this season? Best for the Cubs this decade? Best in the league since the millennium? Try the best starting rotation since the year 1900.

Indeed, as Sahadev Sharma (The Athletic) writes, the Cubs starting rotation has a 56 ERA-. If you aren’t aware what ERA- is, it’s a pitching stat that factors in the run environment, including different parks, leagues, and seasons. So there’s no “Well, they’re good, but offense is down,” argument to be made. The Cubs starting staff has been the very best in baseball since 1900. And, according to Sharma, a few other Cubs teams from the early 1900s follow just behind them. So how the heck are they doing it? Let’s dive in.

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The Cubs starting staff’s ERA is a minuscule 2.29 to this point in the season, which is the best mark since the dead ball era. In fact, only two other rotations from the last 25 years fall into the top 30 (the 2011 Phillies (Roy Halladay, Cliff Lee, Cole Hamels and Roy Oswalt) and the 2015 Cardinals).

But if you want to know how the Cubs are doing it, you don’t need to dig too deeply, because the answer is right on the surface: they are limiting baserunners. The Cubs starters’ collective WHIP this year is just 0.98. That’s the best mark since the 1908 White Sox and no other team from after 1909 cracks the top ten. Sharma’s article at The Athletic has much greater detail into what’s going on here – and I don’t want to spoil it – so I’ll encourage you to check it out.

But let’s not stop there.

So, okay, Cubs starters are not allowing baserunners; they have a low WHIP. That’s great, but the most obvious next question, then, is ‘Well, then how are they doing that?’  August Fagerstrom has our answer at FanGraphs. Stick with me.

The Cubs have among the lowest ERA and ERA- of all time, and they’re achieving those results by limiting the number of baserunners allowed (WHIP). Of course, WHIP stands for “Walks plus Hits per Inning Pitched.” So let’s start with the first first part: walks. The Cubs pitchers have had good control this season (6.9% walk rate), but that’s hardly close to anything historic. In fact, that walk rate is just the 8th best in baseball this season alone. So that doesn’t explain it.[adinserter block=”2″]

Enter Fagerstrom’s piece at FanGraphs. Fagerstrom notes another way the Cubs starting staff has been among the best ever: having the lowest team BABIP allowed. Before we jump right into it, you might be thinking, is that a good thing? And you’d be right to question it. Fagerstrom makes sure to say as much, as well. The truth is, that having a historically low BABIP is probably at least a little bit skillful and a little bit lucky. Either way, it will help explain how the Cubs have managed to be so good in 2016.

First, let’s start with by looking at the Cubs BABIP allowed in reference to the other teams in the league (as of Thursday):

1. Cubs: .250
2. Dodgers: .265
3. Blue Jays: .279
4. Nationals: .280
5. Indians: .282

So immediately, you can see the Cubs are well above the rest (be it by skill or luck) in terms of BABIP allowed this season. But that’s just one year, yes? Perhaps everyone else is just unusually high? Nope. Here’s what the team BABIPs allowed have looked like since 1961:

1. 2016 Chicago Cubs: .250 BABIP (85 BABIP+)
2. 1999 Cincinnati Reds: .262 BABIP (88 BABIP+)
3. 1975 Los Angeles Dodgers: .245 BABIP (88 BABIP+)
4. 1969 Baltimore Orioles: .243 BABIP (89 BABIP+)
5. 2001 Seattle Mariners: .260 BABIP (89 BABIP+)

As you can tell again, the 2016 Cubs have had by far the best BABIP in a very long time; and even once the era was considered, their 85 BABIP+ remains the best (or luckiest). So, are they the best or the luckiest? That’s what Fagerstrom attempts to find out.[adinserter block=”3″]

Of course, that’s far easier said than done. BABIP is hard statistic to fully grasp, even if it’s easy to understand. We know, for example, that some pitchers are better at inducing weak contract, which will result in lower BABIPs, but also that BABIP tends to normalize, for the most part, given enough chances (the luck component of it all). But there are a few ways a team could actually be better at yielding a low BABIP, and one such way is defensive shifting …

… which the Cubs never do. Well, they do, but the Cubs are actually the second least defensive shifting team in baseball with 267 shifts (behind just the Marlins 236). That said, the Cubs have been one of the most effective shifters, saving seven runs despite using just the second least number of shifts. Perhaps correctly shifting is better than over shifting.

Of course, there’s the fact that the Cubs have had one of the best outfield defenses, in terms of turning fly balls into outs (man, I would have not expected that sentence, at least until Spring Training, when Dexter Fowler made his way back to Chicago), probably helps. As does Jake Arrieta, “King of Weak Contact.” But mostly, the Cubs starters have been among the best in suppressing both exit velocity and distance on batted balls, which makes everything just a bit easier for the defense and a bit more explainable for the BABIP. You should definitely check out Fagerstrom’s article for much, much more.

So, to sum up: the 2016 Cubs starting staff has been among the best in baseball (ever), most of that success has come from limiting baserunners, and they’ve been able to limit baserunners by allowing a historically low BABIP. Some of that is undoubtedly luck, some of that is undoubtedly skill, but all of it is something we can enjoy. The 2016 Cubs. They’re pretty good.