Chicago Cubs starting pitching and impact of high ground-ball rate
By Paul Steeno
What is the connection between the high ground-ball rates of the Chicago Cubs starters and aging?
A study conducted by FanGraphs revealed ground-ball pitchers on average age worse than other types of pitchers which has major implications on the Chicago Cubs starting rotation.
According to a graph constructed by FanGraphs writer Jeff Zimmerman, pitchers who surrendered a high percentage of ground-balls gave up more runs on average (as compared to their peak ERA/nine innings) at an earlier age than other types of pitchers.
The y-axis represented change in runs allowed per nine innings (RA/9) and the x-axis represented age. The blue line represented the aging curve of sinker-heavy pitchers (utilizes a sinker on at least 30 percent of pitches), the red line represented the aging curve of pitchers who have a ground-ball rate of more than 50 percent and the green line represented the average aging curve of all MLB pitchers. The results aren’t hard to interpret.
"Right around 30 years old, ground-ball guys start to age worse. They add four runs to their peak RA/9 two years earlier than the average pitcher. The attrition is much worse, too: between 32 and 34 years old, 34% of all innings pitched leave the game, while 74% of all innings pitched by plus ground-ball pitchers disappear.—-Content created by FanGraphs writer Eno Sarris"
The Chicago Cubs have three pitchers in their starting rotation over the age of 30 (Jake Arrieta turns 30 before the 2016 season begins) who also recorded ground-ball rates above the league average of 44 percent (data from 2002-2015). Arrieta had a 56.2 percent ground-ball rate in 2015, while teammates Jon Lester and John Lackey had a 48.9 and 46 percent ground-ball rate respectively. Arrieta tied for fourth highest ground-ball rate among all MLB pitchers in 2015.
The results of this study are interesting when applied to some of the Cubs starting pitchers. Jon Lester, John Lackey and Jake Arrieta are all predominately ground-ball pitchers. Thus far in their respective careers, John Lackey and Jon Lester have defied the law of averages in terms of the aging curve of ground-ball pitchers, while the verdict remains out on whether Arrieta can do the same.
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Jon Lester had the best season of his career in terms of RA/9 in 2014. He had a collective 3.12 RA/9 in his time with the Boston Red Sox and Oakland Athletics despite turning 30 years old before that season began. According to the data FanGraphs compiled, 30 is the age when most ground-ball pitchers begin to see regressions in their performances. Last year with the Cubs during his age 31 season, Lester compiled a 3.64 RA/9 which was just over a half a run more than his peak RA/9 performance in 2014. His 3.64 RA/9 number last season was also lower than his career RA/9 average of 3.81.
Lackey’s situation is more complicated. The veteran right-handed pitcher enters his age 37 season in 2016, yet he comes off a 2015 campaign where he recorded his best RA/9 and ERA of his career at the age of 36. Prior to that, his numbers followed closely with the aging curve offered by the folks at FanGraphs until 2013-2015 when his RA/9 number were all below his career average(albeit only slightly in 2014).
Both players have defied this aging curve to varying degrees, and the Cubs banked on the fact that they would continue to defy it when both players signed their free-agent contracts with this ball club. In his age-30 season in 2016, Arrieta will test this ground-ball pitcher aging curve theory next season.
Last season, Arrieta won the National League Cy Young Award after recording 22 wins and a 1.77 ERA. His 0.75 ERA after the All-Star break was an MLB record. Can the Cubs expect the bearded right-hander to reciprocate these numbers over the next few seasons? Whether he can defy the ground-ball pitcher aging curve like his rotation counterparts could determine the nature of his next contract.
The Cubs are fortunate to have Arrieta under team control until after the 2017 season. The next two seasons, especially 2016, should serve as a tryout of sorts for Arrieta. The Cubs need to see if his career trends towards following this aging curve before signing him to a huge extension.
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Obviously, there is a caveat here: his numbers were so good last season he probably will not reciprocate them. If his numbers over the next few seasons are similar to or better than the 2.53 ERA, .989 WHIP and 10-5 record he posted in 2014, then the Cubs can feel more comfortable signing him to a longer and pricier contract. However, the Cubs shouldn’t sign Arrieta to a long-term contract if his numbers appear to be on the decline no matter how well he pitched in 2015.
The aging curve of ground-ball pitchers is pertinent to the Chicago Cubs organization because three of its key starters recorded above average ground-ball rates last season. This curve shows the risk of signing pitchers over the age of 30 to long-term contracts. The law of averages based on the aging curve developed by FanGraphs suggested that ground-ball heavy pitchers experienceed significant regressions in performance once they hit the age of 30.
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Although total regression hasn’t happened yet to neither Lester nor Lackey, these guys are the exceptions not the rules. The Cubs need to keep this in mind as they decide what to do with Jake Arrieta.