The 2015 season is over and Jake Arrieta has been crowned the NL Cy Young award winner. The pitcher helped lead the Chicago Cubs to the NLCS in what is likely a sign of things to come for the young team. Ian York examines Arrieta’s repertoire to show what sets him apart from the competition.
Jake Arrieta reached the big leagues in 2010 with high expectations, which he completely failed to meet. He was a worse than mediocre pitcher as a rookie, and he remained worse than mediocre through 2013. In 2014, though, he abruptly became a very good pitcher, and in 2015 he received a well-earned Cy Young award as the best pitcher in the National League, with an ERA+ of 222. While no single overnight change led to his success, a big part of it has been his slider.
Arrieta throws a standard major-league repertoire: four-seam fastball (called “FF” by PITCHf/x), two-seam fastball or sinker (“SI”), changeup (“CH”), curve (“CU), and slider (“SL”). As is common, the distinction between his four-seam and sinker is blurry and PITCHf/x labels are fairly arbitrary; here I have recategorized his pitches manually to improve the classification.
Since his debut, Arrieta has changed his pitch mix in a couple of ways. From 2011 to 2012, he started using his sinker more than his four-seam, and by 2015 his four-seam has become almost an afterthought, thrown less than 8% of the time. And from 2013 to 2014, correlating to his emergence as an ace, he nearly doubled his slider use, going from about 15% to nearly 30% of his pitches (this is using Brooks Baseball’s identifications, which are very similar to mine.)
If we look at pitch speed since 2012 (in this case compared to horizontal movement), another trend becomes clear: Arrieta has been throwing harder each year:
His fastballs have respectable – though not extraordinary – velocity, but his curve and changeup, and especially his slider, are thrown much harder than league average. Here are his pitches compared to the rest of the league (dashed lines):
When a pitch is thrown faster, it almost invariably loses movement. Arrieta’s slider has lost some movement compared to his earlier version, but not too much – considering its velocity, his slider has exceptional movement. Here is average break length vs. speed for all pitchers in 2015. I have included both sliders and cutters in this, since a cutter is approximately a slider with more velocity and less movement (for example, FanGraphs classifies Arrieta’s slider as a cutter). Arrieta is the red dot:
Only one pitcher (Garrett Richards) throws a cutter that is faster and has more movement than Arrieta’s slider.
Arrieta’s slider is not the only reason for his success. All of his pitches are excellent; FanGraphs ranks both his fastball and his slider (their cutter) as the most valuable in their category among qualified pitchers, with his change and curve both ranking 7th. Location, command, and strategic mixing of his pitches are all part of his effectiveness. Still Arrieta’s increased use of his improved slider aligns well with his newfound success, and probably is a big part of the cause.