Chicago Cubs: Is a decline imminent for Jake Arrieta?

2015 National League Cy Young Award winner Jake Arrieta took a step, albeit a small one, backward last year. Heading into a contract, looking at his future production is more important than ever for the Chicago Cubs.

A devastating cutter helped Jake Arrieta lead the Chicago Cubs to the postseason in 2015, as part of a historical 22-win campaign. During the second-half, the right-hander went 13-1 with a 1.60 earned run average; one of the best stretches by any pitcher in big league history.

He beat out Los Angeles Dodgers ace Clayton Kershaw for the league’s top pitching honors, thanks largely to that dominant second half. Entering 2016, the question on everyone’s mind was: could he possibly do it again?

In short, we found out the answer was no. He struggled with control, badly at times, and he lost his reliance on his cutter, throwing it nearly 33 percent of the time less than the year prior.

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Still, Arrieta’s 2016 campaign was nothing to scoff at. He won 18 games, pitching to a 3.10 ERA in 31 starts for Chicago. He actually limited hitters to a dozen fewer hits than in his 2015 Cy Young season, but surrendered six more long-balls in the mix.

I’ve never been big on advanced metrics, but decided to dig a little deeper into Arrieta’s 2016 campaign than just the usual numbers we see on television broadcasts.

A closer look at the work turned in by Arrieta

First, I decided to look at Arrieta’s ground ball percentage. It’s nothing too complicated, but given how often he threw his sinker to hitters, it seemed relevant.

According to Brooks Baseball, the 31-year-old’s offspeed pitches were some of the best in baseball at inducing balls hit on the ground – while his fastball has the ability to both whiff hitters and put them away swinging.

"His sinker generates an extremely high number of swings & misses compared to other pitchers’ sinkers, has well above average velo and has little sinking action compared to a true sinker. His slider is thrown extremely hard, results in many more groundballs compared to other pitchers’ sliders and has less than expected depth. The curve is a real worm killer that generates an extreme number of groundballs compared to other pitchers’ curves, generates more whiffs/swing compared to other pitchers’ curves, has a sharp downward bite and is slightly harder than usual."

But when you look at Arrieta’s ground ball percentage from 2014 to 2016, there’s not a clear link between the number and his success on the mound. His best numbers in Chicago actually came in 2014, when he posted a 51 percent clip. In his Cy Young-winning season, that number rose to 58 percent, before evening out at 54 percent in 2016.

A benefactor of the league’s best defense?

The next measure examined was DRA, a metric employed by Baseball Prospectus.

"By accounting for the context in which the pitcher is throwing, DRA allows us to determine which runs are most fairly blamed on the pitcher."

Similar to his ground ball percentage numbers, Arrieta saw his DRA actually increase from 2014 to 2015, from 2.42 to 2.89. Granted, that was over a much larger sample size (229 innings as opposed to 156 2/3), but the results were clearly worse.

Last season, he saw a dramatic increase, going from 2.89 all the way to 4.02. You saw a similar increase in his FIP (fielding independent pitching), as well – 2.38 to 3.56. As you can imagine, his ERA jumped by nearly 1.5 runs. He ended the year at 3.10 after his sterling 1.77 mark in 2015.

Why the increase? If you look through the data, there is one glaring culprit: his offspeed stuff

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simply was not as effective as it was in the year prior.

Opposing hitters squared it up better. From 2015 to 2016, opponents saw their slugging percentage against his breaking pitches more than double from .094 to .217. It’s still not a remotely close to an eye-popping number, but regardless, any time a figure like that doubles, it’s worth taking note.

Arrieta saw his overall velocity fall over the last two years, as well. Per Baseball Prospectus, his peak velocity fell from 97.0 to 96.3. That being said, the year prior, he came in at just 95.9 mph. Again, it’s hard to draw a clear line connecting this to his effectiveness.

What’s in store for the Cubs’ right-hander?

PECOTA projections say these trends will continue in 2017 and beyond. His earned run average and fielding independent pitching will both tick up from last season. His ground ball percentage takes a big hit as well, dropping from 56 percent all the way down to 44 percent.

Rather than getting back to the form we saw in his historic campaign two years ago, control issues seem likely to remain, based on forecast models. He’s projected to win just 13 games, allowing 20 home runs – up from his 16 dingers a year ago. The same measures believe he’ll put up roughly the same walk totals in his starts this year.

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I don’t know if I’d call what the  Cubs will get from Jake Arrieta in 2017 a regression. In fact, it’s largely close to the same performance we saw from him during the World Series run.

The simple truth is this. Arrieta isn’t an ace. In fact, he’s not even the best pitcher on the Cubs’ starting rotation. His delivery requires intense physical demands and will only become more difficult as time passes. He’ll be a solid member of Chicago’s staff in 2017 – but with what he’s seeking in a contract, it’ll be his last season on the North Side.