Seeing the Future of the Cubs Defense

The Cubs won the World Series. I’m sure enough has been made of that. I’m not sure enough has been made of their defense. Or, if you prefer, their hit suppression. Don’t get me wrong, there have been articles about this very topic. But, you know BABIP. By BABIP allowed, the 2016 Cubs were the all-time best. The all-time best, over more than a century. It’s kind of unbelievable what the Cubs pulled off.

Like many statistics, league BABIP changes with the eras. You don’t want to compare raw BABIPs throughout history, just as you wouldn’t want to compare raw strikeout rates, or slugging percentages. I’ve calculated something very simple — the difference between a team’s BABIP allowed and the league-average BABIP allowed. Here’s a table of the top 10 since 1900, and, well, I told you:

The Cubs just finished 43 points better than the average. They were 27 points better than the next-best team in 2016. And in this table, which spans the entirety of what I’ll just call meaningful modern baseball, the Cubs are in first place, and by seven points. Seven points separate second and eighth. Internalize this, because it is crazy. What made the Cubs so very good? Yeah, the lineup was productive. Yeah, the pitchers could get their strikeouts. But the pitchers also limited hard contact, and the defenders were everywhere. Outlier seasons like this are extremely uncommon.

At the end of this post, I’m embedding a poll. But this isn’t another one of my polling projects — this is more of a one-off. I just want to see what the community thinks the Cubs’ BABIP allowed is going to be next season. I know you don’t know. I know the Cubs don’t know. But I want to see how much of this you believe in, because, again, the Cubs just ran the best adjusted BABIP of all time.

Before we get to the poll, we should review what we have. Perhaps unsurprisingly, the Cubs’ hit suppression was fairly consistent. I went through the team pitching game logs and calculated rolling averages of their BABIPs allowed over 15-game stretches. Here’s that plot, with the league average included for reference:

Every so often, you see the Cubs get close to the gray dotted line. The two lines almost touch! But over no single 15-game stretch did the Cubs allow even a league-average BABIP. That’s one of the things that made their postseason modestly surprising. I mean, it wasn’t surprising in that the Cubs won it all, but here is a table:

The postseason Cubs were actually below-average, in these terms. They won! Nobody cares! Yet that definitely bucked the established trend. The Cubs’ worst regular-season month here was July, when their BABIP allowed was still 26 points better than the average. Then you’ve got April, with a difference of 37 points. Things got more extreme from there.

When you think about the Cubs moving forward, you see how consistent they were in 2016. That might factor into your 2017 expectations. What sort of BABIP are they going to allow a season from now? They’ll return Jon Lester, Jake Arrieta, and Kyle Hendricks. All three of those pitchers just suppressed quality contact. And as the defense goes, so much will stay in place. The systems and strategies will stay in place. There’s still going to be Anthony Rizzo, and Kris Bryant, and Addison Russell, and Ben Zobrist, and Jason Heyward. There will probably still be Javier Baez. It’s going to be a similar unit, if not an identical unit. You’d think their true talent shouldn’t slip too much.

But we should consider other evidence, too. The easiest assumption is that, since so much of the personnel will stay the same, the performance should stay about the same. Six months of baseball is a long time, right? Yet you always have to think about regression to the mean, with any sort of extreme data point. Here’s a plot of year-over-year team BABIPs allowed, compared to the average. So you’ve got the BABIP differences in Year X, and the BABIP differences in Year X + 1.

It shouldn’t be at all surprising to observe a relationship. Teams with good defenders tend to retain good defenders. Teams that allow more hits tend not to fix everything in one winter. The slope is what’s important here, and it suggests the average defense regresses toward the mean by about 57% the next season. Regression is a powerful phenomenon. It likes to show up everywhere.

Let’s focus on just the best defensive units. Excepting the Cubs, the top 10 BABIP teams were 31 points better than average. The next year, those same teams were 16 points better than average. The numbers for the top 25 BABIP teams are 28 points and 15 points. The numbers for the top 50 BABIP teams are 26 points and 13 points. Even the best teams have given back about half of their advantages. As a recent example, the 1999 – 2000 Reds went from being 36 points better than average to 14 points better than average. The 2001 – 2002 Mariners went from being 32 points better than average to just five points better than average. It’s something to keep in mind, just as you should also keep in mind how many of the same players the Cubs are bringing back.

On the one hand, there’s the truth that regression is inescapable. Baseball’s own history provides evidence of that. Additionally, it’s hard to imagine that, in the year 2016, any one baseball team could be so much better than anyone else. Some of that had to be a fluke, right? Yet we’re talking about a team that set a record. Maybe not a sexy record, maybe not a record you’ll ever talk about in a bar, but it’s a record of real significance. Because of their pitchers and because of their defenders, the 2016 Cubs were death to balls in play. So many of the key players are going to be returning. How much are they going to give back, really? How much credit do they deserve for six months of remarkable consistency?

We’ve never seen this. Not to this extent. You’ll forgive my uncertainty. Maybe we can all reach an agreement together.