What's Up With Jake Arrieta?

Is the Cubs' ace on his way to massive regression, or is this simply just a bump in the road?

When the calendar flips over to July, the dog days of summer are really what tend to separate Major League Baseball teams from each other. And the last 14 days have opened some eyes on the Chicago Cubs.

While I'm fairly certain every Cubs fan would have dreamed for a 51-30 start through the first half of the year, it's what the last 14 games -- prior to their current series against the Reds -- have shown that raises an eyebrow or two. Swept by St. Louis. Lost three of four to Miami. Swept Cincinnati. Swept by New York.

Overall record: 4-10

Over such a long season, there's bound to be ups and downs, and certainly headed into a four-game slate with the Mets and those arms is going to lead to some potentially tough outcomes.

In that difficult 14-game stretch for the Cubs, the team ERA approached a mark close to five, and over the last month or so, no one has been more disappointing on the staff than Jake Arrieta. His run since 2014 has been pretty much other-worldly, so it was bound to not continue. But is it all really that bad? Let's find out.

Recent Struggles

A little closer look reveals about Arrieta and recent command struggles:

Year BB/9
2010 4.31
2011 4.45
2012 2.75
2013 4.90
2014 2.36
2015 1.89
2016 3.50
June 2016 4.82

If you know much about Arrieta's background, he was a highly decorated prospect out of Texas Christian University (TCU), who actually led Division 1 baseball in wins his sophomore season (14). Arrieta was selected in the fifth round by the Baltimore Orioles and commanded a then record $1.1 million signing bonus (highest bonus ever for a fifth-round pick).

He was a largely uninteresting prospect in the Orioles system who bounced around due to -- yup, you guessed it -- command issues. As you can see in the table above, Arrieta had a walks per nine innings hovering in the mid- to high-4s. While he was blessed with an excellent arsenal, he was traded nearly three years ago to the date (July 2nd, 2013) along with Pedro Strop to the Cubs for megastars Steve Clevenger and Scott Feldman.

In 2014, Arrieta's career took off as he got the walks got under control.

But what sticks out now? Well, that walk rate is starting to climb into that scary territory again that we saw from 2010-2013. For an even more granular look, here's a month-by-month breakdown of Arrieta's 2016 campaign. What you will notice is that, as the walks have started to climb, his wOBA, as you would expect as more runners are reaching base, has risen as well:

Month BB/9 FIP xFIP wOBA
March/April 2.50 2.94 3.25 .205
May 3.46 2.60 3.22 .220
June 4.82 2.77 3.57 .289

But Is It All That Bad?

While the walk rate has climbed recently, it's not as though his FIP, xFIP and wOBA against have been horrendous.

Adding earned run average (ERA) to the table above -- and removing wOBA -- helps quantify this picture a little more clearly:

March/April 2.50 1.00 2.94 3.25
May 3.46 2.08 2.60 3.22
June 4.82 3.54 2.77 3.57

As you can see, Arrieta sported outstanding earned run averages in the months of March, April, and May, and when compared to both FIP and xFIP, it's obvious that he was performing well above expectation. In June, though, you'll notice that his FIP is actually lower than March/April, with an elevated ERA. Meanwhile, his xFIP has changed, but not substantially.

In other words, there's a good chance this is just simple regression. That seems to be true -- Arrieta was the beneficiary of an extremely high left-on base percentage (LOB%) in March/April (95.2%). That was sure to fall, and it did, as his LOB% went to 78.3% in May and 71.8% in June.

Meanwhile, his opponents' batting average on balls in play (BABIP) has risen each month of the year, starting at .188 in March/April, moving to .235 in May, and then hitting .319 in June. His season-long BABIP is now .251, which is just six points higher than last year's mark.

Naturally, the left-on-base and BABIP numbers will lead to a higher ERA, which is why it's picked up there but not within FIP or xFIP.

Here's maybe a slightly different look to support Arrieta's outstanding work in every month of the season:

Month K% K-BB% Hard Hit %
March/April 24.8% 17.1% 20.7%
May 27.0% 17.6% 21.2%
June 29.5% 17.2% 24.3%

So while the walks have indeed continued to climb as noted above, so have the strikeouts. The hard-hit rate has risen slightly, but not to the point of panic. Arrieta's numbers show that he's still among the game's elite starting pitchers.

Simmer Down, Cubbies

Arrieta will be fine for the remainder of 2016 -- recent performance has suggested that this is all regression-related given that there hasn't been a noticeable dip in his hard-hit rate, his FIP, and his xFIP. And his strikeout rate has continued to rise in conjunction with a slightly elevated walk rate.

This is definitely a bump in the road and not a detour, and as long as the offense keeps chugging along, the league's best team ERA (3.16) will sure to come back to form, too.