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Examining Jake Arrieta's subpar playoff starts

For the first time in months, Jake Arrieta was surprisingly average in back to back starts. Is there any reason for the Cubs to be worried?

Robert Deutsch-USA TODAY Sports

Jake Arrieta has given up four runs in each of his last two playoff starts. Before that, he hadn't given up four runs in a single start since June 16th, and he hadn't given up four runs in back to back starts since the end of May. These two games have caused some Cubs fans to worry, which is a testament to how good Arrieta had been prior to his NLDS start against the Cardinals.

Before I dive into the data to see if there is anything to be concerned about from Arrieta's last two outings, I thought it would be helpful to remind people that the number of runs a pitcher allows can be affected by factors like sequencing and batted-ball luck. These kinds of factors make it difficult to know how good a starting pitcher is based on just two starts. In larger sample sizes, these factor tend to balance out, giving us a better sense of a player's true talent level. It is quite possible that the Jake Arrieta who put himself in the Cy Young conversation with a strong regular season is no different from the Jake Arrieta who has struggled in his last two starts (in fact, there's a decent chance that is the case).

Over his last two starts, Arrieta has faced 46 batters in 10 2/3 innings, allowing nine hits, four walks (one intentional), and one hit batsman, all while strikeout out 17 (38 percent of the batters he has faced). On the surface, these numbers are pretty strong. His strikeout and walk totals are consistent with his regular season numbers, and he isn't allowing an alarmingly high number of baserunners.

The biggest problem for Arrieta is that the nine hits he has given up include three doubles and two home runs. Oftentimes, extra base hits are the result of a pitcher missing his spot and catching too much of the strike zone, and this is partly true for the hits given up by Arrieta.

Here is the strikezone plot from David Wright's first inning plate appearance, which resulted in a double.

All four pitches of the at-bat were sinkers between 93 and 95 MPH. After falling behind 2-1, Arrieta threw a poorly located sinker near the middle of the plate, and Wright pounded it off the wall in center field beyond the reach of Dexter Fowler.

Here's the plot for Jhonny Peralta's double against Arrieta in Game 3 of the NLCS.

After throwing two sinkers and getting ahead of Peralta 0-2, Arrieta hung an 88 MPH slider up in the strike zone on the outer half of the plate, and Peralta belted the offering off the ivy in left field. Given the situation as well as Peralta's skill as a hitter, it seems unlikely that Arrieta intended to throw the pitch in that particular location.

So it appears as though we have two mistake pitches from Arrieta and two predictably bad results. The two home runs he gave up tell a different story, however.

First, here is Jason Heyward's home run in Game 3 of the NLCS.

Then we have this home run by Daniel Murphy from Sunday night.

Interestingly enough, neither of these pitches was in the strikezone, with the pitch to Heyward a few inches off the outside corner of the plate, and the pitch to Murphy more than six inches below the knees, according to the PITCHf/x data on Brooks Baseball. In other words, it is hard to call either of these pitches a mistake given their location. These simply appear to be cases where the hitter deserves most of the credit for what happened. Heyward took the ball the other way, lofting it into the jet-stream that was present at Wrigley Field that night, while Murphy golfed his pitch down the right field line, tucking it barely inside the foul pole. Sometimes, good pitchers make bad pitches and get bad results, and sometimes they get bad results even when they don't make bad pitches, and Arrieta has been hurt by both of these situations recently.

Some will point to Arrieta's decreased velocity from Sunday night as a reason for concern. It is true that the average velocity on his sinker in his start against the Mets was 93.7 MPH, the lowest of any start this season. WIth Arrieta at 248 2/3 innings this season (postseason included), it is possible that he may be getting worn down, especially since he hasn't pitched more than 175 innings in any season of his career.

However, as Dave Cameron pointed out yesterday, Arrieta's decreased velocity may have been a result of the unusually cold weather at Citi Field (the game time temperature was 45 degrees). It is also worth pointing out that Arrieta's sinker velocity was a healthy 94.8 MPH in his previous start against the Cardinals, which is barely below his season average of 95.2 MPH. If Arrieta is getting worn down, he hasn't shown it until very recently. After all, he just finished putting up an historic second half of the season, and he showed no signs of decline at point during that stretch.

Even the best starters can have two bad starts, especially against good lineups in the playoffs, and we have finally seen this happen to Jake Arrieta. While it may be worthwhile monitoring his velocity going forward, we will need to see much worse from Arrieta before we should start to get worried.

Nick Lampe is a contributor at Beyond the Box Score and Viva el Birdos. You can follow him on Twitter at @NickLampe1.