In Jake Arrieta's last start against the Pirates, he pitched to the tune of 8 innings of 1 run ball with 5 strikeouts and approximately a 72% ground ball rate.
Since the All-Star break, he has pitched at an otherworldly level and has put himself into the Cy Young discussion.
The question is how has Jake Arrieta become so good?
Well, the answer to this question stems from ground balls, ground balls, and more ground balls. Based on ERPA (Earned Runs Prevented on Average), Jake Arrieta is ranked in the top five for all starting pitchers in the Majors for run prevention.
This is not because he is striking out batters at a ridiculous level, but more from his ability to induce a ton of ground balls.
Over his short tenure with the Cubs, he has developed a "sick" four-pitch combination for inducing weak contact: a sinker, a slider, a cutter (although he calls it a different kind of slider), and a "power" curveball.
Figure 1: Top 10 ERPA for all Starting Pitchers
In 2013, Arrieta posted an unimpressive ERPA of 0.75 over the course of 75.1 innings with a 40.4% ground ball rate.
In 2015, he has, thus far, posted an ERPA of -1.59 with a ground ball rate of 55%.
It is important to continuously stress that high ground ball rates are essential for high run prevention because ground balls mean, for the most part, that the pitcher is inducing weak contact.
Jake Arrieta’s development into a heavy ground ball pitcher can be explained by the introduction of his cutter, which he calls a different kind of slider.
As you can tell from Figure 2 below, his slider has a high variation in horizontal and vertical breaks. One slider can have a horizontal break of ~ -1' and a vertical break of ~ 10'.
While, another slider can have a horizontal break of ~ -5' and a vertical break of ~ 0'.
While, both these pitches are classified as sliders. In actuality, the former should be considered more of a cutter.
While, the latter should be thought of as a slider. In 2013, in his stints with the Orioles and Cubs, Arrieta only used an inconsistent high 80s slider (Figure 3).
As mentioned in an article by Eno Sarris, Arrieta has learned to manipulate the slider to have different breaks for different situations.
In the case of his last start against the Pirates, Arrieta was able to force Gregory Polanco, a lefty, to induce a broken bat, weak ground ball (Gif 1).
In this situation, Arrieta threw a 92 mph cutter with an elevated vertical break and lower horizontal break.
If we think about his slider as two pitches, he has been able to keep hitters guessing and induce more ground balls because of his wide pitch selection.
Figure 2: All Sliders in 2015
Figure 3: All Sliders in 2013
GIF 1: Jake Arrieta vs. Gregory Polanco on September 16th
Unless Zack Greinke suffers a late season meltdown, Jake Arrieta probably will not win the Cy Young because of the vote not using any advanced quantitative justification.
However, by introducing a situational slider that can be a cutter and be a traditional slider, Arrieta will prove to be a top pitcher in the Majors for years to come.
As his second half results of 0.95 ERA and a 62.1% ground ball rate show, his consistency has proven crucial in the Chicago Cubs' run to the postseason.
References:
1. "Baseball Reference." Baseball-Reference.com. Baseball Reference, n.d. Web. 14 Apr. 2015.
2. "Baseball Statistics and Analysis | FanGraphs Baseball." Baseball Statistics and Analysis | FanGraphs Baseball. N.p., n.d. Web. 24 Apr. 2015.
3. Sarris, Eno. "Jake Arrieta’s One-Grip Multi-Slider | FanGraphs Baseball." Fangraphs. N.p., 18 Mar. 2015. Web. 18 Sept. 2015. .
I would highly recommend reading the link above.
In the article, Eno Sarris discusses with Jake Arrieta about manipulating a slider to have different kinds of breaks for different situations.
In my opinion, this type of situational pitching is overlooked in analytics and should be explored in its effectiveness.
NOTE: All statistics accurate as of 09/18/15
By Sanjay Pothula
AriBall.com
