Jake Arrieta: From Afterthought to Ace

In 2015, Jake Arrieta has without a doubt been one of the very best pitchers in baseball. However, before his nationally televised no hitter on Sunday, Arrieta was not getting quite as much recognition on a national level as he has deserved, based on his stellar performance. Frankly, Arrieta has been pitching at an elite level since 2014, and should currently be considered one of the front- runners for the NL CY Young this season. Let’s examine how the 29 year old righty has gotten to this point, and how his statistical profile has changed over the years, eventually progressing to the lofty standards it’s at right now.

Arrieta made his major league debut with the Orioles in 2010, and through 100.1 IP, he was not very effective, with a dismal 52/48 K/BB ratio, 4.66 ERA, and a 5.17 xFIP that season. In 2011 Arrieta was not much better in 119.1 inning pitched, although his K% did increase from a pretty dismal 11.6% in 2010 to a much more respectable 17.8%. However, his 5.05 ERA and 4.52 xFIP were both still underwhelming.

In 2012, Arrieta’s peripherals were actually very good through 114.2 innings, where his K% went up all the way up to 22%, and his BB% decreased to 7.1% (from 10.7% and 11.3% in 2010 and 2011, respectively).   Despite these obvious improvements, Arrieta was very unlucky, and his peripherals did not translate into the type of results that usually go along with them.

He produced an abysmal 6.20 ERA that season, but clearly, most of it was due to bad luck, as he had a LOB% (left on base %) of 57.3%, which is far below the league average of roughly 72%, and a HR/FB% of 14.5%, which is also far above the league average of roughly 9.5%. LOB% and HR/FB% both tend to regress towards the mean, and Arrieta’s xFIP of 3.65 (xFIP normalizes HR/FB% and is void of hits allowed sequencing, therefore nullifying Arrieta’s incredibly low LOB%) clearly shows how much better his season could have/should have been.

Although Jake’s unlucky, yet abnormally high ERA in 2012 may have scared off some teams, and surely kept him from getting any national recognition, his very strong peripherals and solid 3.65 xFIP clearly made him a low risk, buy low candidate for many saber- savvy front offices around baseball. Theo Epstein, who was only in his second season leading the Cubs in 2013, clearly took notice and acquired Arrieta in a midseason trade as part of a package for Scott Feldman. Despite Jake’s peripherals actually getting worse in 2013 through 75.1 innings split between the two clubs (4.61 xFIP, 18.5% K%, 12.7% BB%), and him spending much of the season in the minors, the rebuilding Cubs had clearly taken notice, and were about to give Arrieta a major chance in 2014. This would be a decision they would not regret.

In 2014, Jake Arrieta simply broke out big time, to put it bluntly. In 156.2 big league innings, he produced a spectacular 2.53 ERA (which was tenth best in the major leagues for pitchers with over 150 IP), with the peripherals to back it up. He posted a career high 27.2% K% and a career low 6.7% BB%. Arrieta’s 20.2% K%-BB% was the eighth best in the big leagues for pitchers with at least 150 IP. His 2.26 FIP actually ranked second in the bigs for pitchers with over 150 IP, and his 2.73 xFIP placed him sixth best.

Arrieta’s GB% (ground ball%) also increased dramatically in 2014, up to 49.2% from 40.4% in 2013, which set a new career high.   Arrieta now profiled as a hard throwing (average fastball velocity of 93.4 mph, per PITCHf/x) groundball pitcher who strikes out a high percentage of batters and also limits walks. That is a strong combination that tends to be a successful one, and his newly found success (although not entirely unexpected if one were to look at his peripherals from his 2012 season, where he pitched well despite a very high ERA that was mostly due to poor luck) has continued in 2015.

Through 183 innings this season, Arrieta has a 2.11 ERA (second best in the big leagues out of all qualified pitchers), 2.49 FIP (third best), and a 2.73 xFIP (fifth best), along with a 26.8% K% (ninth best), 6.2 BB% (just outside the Top 30, but still very impressive for any pitcher, especially one who posts such a high K%), and a 20.6% K%-BB% (tenth best). His 5.4 fWAR also ranks him fourth in the big leagues amongst pitchers, behind Clayton Kershaw, Chris Sale, and Dallas Keuchel.

There have been some fundamental changes that have taken place when one looks even deeper into Arrieta’s pitching profile since 2014. Arrieta has continued his trend of being more of a groundball pitcher, as his GB% has once again increased from 49.2% in 2014 to 53.7% in 2015. His FB% (fly ball%) has, in turn, decreased from previous levels, from 34.3% in 2013 to 28.4% in 2014 and finally, to 24.1% so far this season.

Although his Zone% (% of pitches seen in the strike zone) has stayed roughly the same throughout his career (48.2% so far in 2015; it has always been between 47% and 50.7% in his career), his opposing hitters’ Swing% reached a career high in 2014 of 45.5%, and increased even further this season to 46.6%. This is true of both O-Swing% (% of pitches a batter swings at on pitches out of the zone), which has peaked at 32.9% in 2014 and 31.8% so far this year, and Z-Swing% (% of pitches a batter swings at on pitches in the zone), which improved to 59.6% in 2014 and up to a career high of 62.4% in 2015.

Batters have also made less contact in the past two seasons, as their Contact% has been at 76.9% and 77.2% in 2014 and 2015, respectively. Before 2014, batters’ Contact% against Arrieta had never been below 80.5%. Batters have made less contact on both pitches outside the zone (O-Contact%), where he set a career best (lowest) so far in 2015 at 61%, and in the zone (Z-Contact%), where he’s also set a career best (lowest) this season so far at 86%. He has also set a career high in average fastball velocity in 2015, with an average of 94.2 mph. (All of this data is per PITCHf/X).

His no hitter on Sunday may have finally given Jake Arrieta enough national recognition to be placed in the conversation for the NL CY Young in 2015, in what looks to be a close competition between Arrieta and other pitchers such as Zack Greinke, Clayton Kershaw, Jacob deGrom, and Gerrit Cole. Since 2014, he has clearly been one of the best pitchers in all of baseball, and his peripheral numbers indicate that he is no fluke.

Arrieta’s emergence as a bonafide ace shows the value of looking past surface statistics like ERA to gauge how well a pitcher is truly pitching, and how well they could be expected to pitch in the future. Sometimes, as happened to Arrieta in 2012, a pitcher’s peripheral numbers show that he has allowed more runs than he should have, due to unlucky breaks such as bad hit sequencing (usually evident in a high LOB%) and high HR/FB% that tend to regress towards the mean.

Smart front offices, like that of the Cubs, keep an eye on players like this, as often times their ERAs start to resemble their peripherals (such as ERA estimators like xFIP) as luck evens out. In Arrieta’s case, his peripherals improved even further in the past two seasons upon their impressive 2012 rates, turning him into one of the best pitchers in baseball.

However, even when peripherals don’t improve as extremely as Arrieta’s did, smart front offices can still use a players’ poor luck to acquire a valuable asset for a relatively low price. That is exactly how some teams get, and stay ahead, and why some rebuilding efforts progress much quicker than others. The pitcher may not become a CY Young contender like Arrieta, but oftentimes still becomes a serviceable pitcher worth more than his salary.

Acquiring players like this is how smart front offices avoid over paying for much of their roster in the ever- so- expensive free agent market. Once in a while, they get even better than could’ve reasonably been expected, and become stars.