After getting swept by the New York Yankees and losing two out of three to the Colorado Rockies, the Chicago Cubs are now sitting on a .500 record. By run differential or BaseRuns expected performance, tools that strip out sequencing, the answer is the same; the Cubs have played pretty much like a .500 team. The offense has been a little worse than average, the pitching a little better than average, but overall, the team has played roughly like an 81 win team so far.

Of course, this isn’t what recent Cubs teams have played like.

In 2015 and 2016, Cubs starters topped all of Major League Baseball with 36.3 WAR, just ahead of the Nationals, Mets, and Dodgers. The starters’ 3.50 FIP, without even considering the impact of defense or the potential of inducing weak contact, has been the best in the majors. The Cubs have returned almost all of last year’s staff intact, with Jon Lester, Jake Arrieta, Kyle Hendricks present for each of the past two seasons and John Lackey around last year.

The question we are trying to answer here is what is responsible for the downturn in results. We are just 34 games into the season, so we could chalk it up to luck. We could try to determine if the talent level has changed in any way, which might cause us to lower our expectations, and we could point to some outside factors that aren’t luck, but aren’t necessarily the responsibility of the pitchers, like defense. To frame our understanding of what is going on, it probably helps to create some expectations of what we would expect to see from a Cubs rotation this season. While Brett Anderson has made six starts, he’s only pitched 12% of the Cubs starter innings, and little was expected of him, so we will focus on the four returnees.

First, let’s take defense or inducing weak contact out of the question. Below we see the FIP for each pitcher from last season, this season, and our Depth Chart projections at the beginning of the season.

Cubs Starters from 2016 to 2017 2016 FIP 2017 Proj FIP 2017 FIP Jake Arrieta 3.52 3.38 3.78 Kyle Hendricks 3.20 3.57 4.24 John Lackey 3.81 3.87 4.17 Jon Lester 3.41 3.38 3.58 AVERAGE 3.49 3.55 3.94

Without accounting for defense, it looks like the Cubs are pitching a bit worse than they did last season. Part of the problem is the Cubs don’t have any pitchers over-performing at the moment, though when all of the pitchers have good projections, that can be difficult. Now let’s compare the above to ERA.

Cubs Starters from 2016 to 2017 2016 ERA 2017 Proj ERA 2017 ERA Jake Arrieta 3.10 3.21 5.35 Kyle Hendricks 2.15 3.40 3.40 John Lackey 3.35 3.74 4.29 Jon Lester 2.44 3.25 3.27 AVERAGE 2.76 3.40 4.08

So this table makes it look like the Cubs starters have gone way off the deep end. Here are some of the numbers underlying those changes with numbers from this season and last.

Cubs Starters from 2016 to 2017 Season Name K/9 BB/9 HR/9 BABIP LOB% HR/FB 2016 Jon Lester 8.8 2.3 0.9 .256 84.9 % 12.2 % 2017 Jon Lester 8.7 3.5 0.9 .316 75.9 % 11.1 % 2016 Jake Arrieta 8.7 3.5 0.7 .241 74.9 % 11.1 % 2017 Jake Arrieta 10.2 2.8 1.4 .364 58.5 % 14.3 % 2016 John Lackey 8.6 2.5 1.1 .255 76.2 % 12.9 % 2017 John Lackey 9.9 2.4 1.7 .310 73.7 % 19.0 % 2016 Kyle Hendricks 8.1 2.1 0.7 .252 81.4 % 9.6 % 2017 Kyle Hendricks 7.7 3.6 1.1 .255 78.6 % 15.6 %

Lester is about the same. Lackey seems to be pitching better except for those homers. Arrieta’s strikeout and walk numbers are better, but the homers have gone way up mainly because he has turned into a flyball pitcher in the early going this season. Hendricks’ walks have gone up as have his homers. Both Hendricks and Arrieta have seen fairly sizeable dips in their velocity in the early part of the season which could explain the increase in homers. One part of last season that has not carried over from last year to this point has been the historically low BABIP that the Cubs had as a staff last season. Only Hendricks is duplicating the BABIP from last season with every other member of the rotation seeing a 50-point or more change.

Last year, I posited that much of the Cubs’ low BABIP numbers were due to an incredible defense. Thanks to more searches on Statcast, we can come a little bit closer in that argument. Here are the Cubs’ pitchers xwOBA numbers compared to their actual wOBA from 2016 and their xBA compared to their actual BA in 2016.

Cubs Starter 2016 Statcast Numbers Player xwOBA, wOBA Difference xBA – BA Difference John Lackey 0.312 – 0.281 0.031 0.246 – 0.218 0.028 Jake Arrieta 0.293 – 0.264 0.029 0.224 – 0.194 0.030 Jon Lester 0.278 – 0.266 0.012 0.223 – 0.211 0.012 Kyle Hendricks 0.262 – 0.258 0.004 0.214 – 0.207 0.007

That xWOBA number accounts for any ability the Cubs pitchers might have to induce weak contact, and all but Hendricks still got results much better than expected. This is the impact of defense and luck. Here are the numbers this season.

Cubs Starters 2017 Statcast Numbers Player xwOBA, wOBA Difference xBA – BA Difference Kyle Hendricks 0.337 – 0.296 0.041 0.279 – 0.231 0.048 John Lackey 0.329 – 0.331 -0.002 0.263 – 0.265 -0.002 Jon Lester 0.280 – 0.325 -0.045 0.207 – 0.255 -0.048 Jake Arrieta 0.285 – 0.353 -0.068 0.230 – 0.290 -0.060

The Cubs are not getting that bump they received last season from their defense or some good fortune. In the outfield, the team switched out Dexter Fowler and a combination of players led by Kris Byant for Kyle Schwarber and a combo led by Albert Almora and Jon Jay. Mike Petriello took a look at those switches early on this season and they have not proved beneficial in the early going. Almora should prove to be better than Fowler over the course of the season, but Schwarber is a pretty big downgrade, and they might not get the same production from Jason Heyward, as he currently sits on the disabled list.

Last season created unreasonable expectations for the Cubs in terms of run prevention. The starters are pitching slightly worse on the whole, with the velocity drops of Hendricks and Arrieta the most concerning. The returning starters are pitching a little below expectations, but just one-fifth of the way through the season the numbers aren’t unreasonable. FanGraphs still has the Cubs as the sixth best rotation in baseball, and if Arrieta and Hendricks can figure things out, there’s no reason to think the Cubs won’t be very good going forward. Even with the changes in the outfield, the team should still be solid defensively, so there is room for improvement when it comes to BABIP and the related left-on-base numbers.

Yes, the Cubs’ rotation is underperforming, but it isn’t doing that poorly. Even an underperforming Cubs rotation with their lineup and defense should be enough to win 90 games, and 95 wins is still a reasonable possibility if the team pitches just a little bit better.