Sample size should almost always be considered when dealing with baseball statistics.
For many pitching statistics, one season for a full-time starter (more than 160 innings), is actually a small sample size. Because of this, evaluating individual performances by relievers is rather difficult.
Last year, Josh Roenicke, of the Colorado Rockies, led all pitchers in innings out of the bullpen, with 88.2, a sample size only about half what a full-time starter would throw.
If a reliever throws 60 innings in back-to-back seasons, which is a fair amount out of the bullpen, the overall sample (120 IP) would still be very small.
Only a few statistics stabilize, or become reliable, over a ~60 IP sample:
I’ve found that the small sample that a reliever’s numbers are subject to make future runs allowed extremely difficult to predict.
In that study, I found that many of the more advanced ERA estimators did not do a good job of projecting future runs for relievers.
For me, this was not the most important takeaway from that study. That honor rested with how a reliever’s strikeout percentage beat more established estimators (FIP, xFIP and SIERA) at predicting future runs.
This fact brought me to the idea for this piece.
The random variation that affects ERA, especially for a small sample like one season for a reliever, causes it to not be a very reliable number to help look into the future. Thus, I decided to use strikeout percentage’s predictive ability to look at a few relievers who had higher than average strikeout percentages (K%) and higher than average ERAs in 2012.
My theory is that these pitchers will end up with better run prevention results in 2013.
Here are the 2012 average strikeout percentage, ERA and adjusted ERA (FanGraphs’ ERA-) for relievers:
Using a minimum of 30 innings pitched, I found that 32 relievers had both a higher than average strikeout percentage and a higher than average non-adjusted ERA. Also, 32 relievers had both higher than average strikeout percentage and higher than average adjusted ERA, but the two lists were not identical.
I don’t plan on highlighting each pitcher, but for those who are interested in seeing all of the names, I’ve attached a google doc.
Instead, I’d like to highlight five pitchers who could see a big boost in results out of the ‘pen next season.
2012 numbers: 52 IP, 224 BF, 36.2 K%, 4.33 ERA, 109 ERA-
A Philadelphia Phillies left-hander, Bastardo, posted a superb 2.63 ERA (69 ERA-), in 2011. Bastardo’s ERA was supported by by a .179 batting average on balls in play (BABIP), and a 81.1 percent left-on-base rate.
Both of those numbers regressed in 2012 (.306 BABIP, 72.5 LOB%) and his ERA ballooned.
Interestingly, Bastardo’s strikeout percentage improved by over five percent and his ground ball percentage improved by over two percent, while his walk rate (11.6 percent) remained constant.
Among relievers (minimum 30 IP), Bastardo ranked sixth in strikeout percentage, ahead of the likes of David Robertson and teammate Jonathan Papelbon, yet his adjusted ERA was 18 percentage points above league average.
If Bastardo’s strikeout percentage is any indication of what the future holds, then the Phillies could receive some serious value from the lefty, who is projected to make only $1.1 million next season.
2012 numbers: 69.1 IP, 310 BF, 30.0 K%, 4.67 ERA, 118 ERA-
The Brewers’ closer, Axford, was one of the best relievers in baseball in 2010 and 2011. Over those two seasons, he racked up 70 saves, while posting a 2.18 ERA and 2.29 FIP. Axford saved 35 games in 2012, but the results weren’t nearly has good.
Axford blew nine saves (he had only five career blown saves coming in), and his adjusted ERA and FIP (104) were significantly lower than league average.
His strikeout numbers were very good and right around his career average (29.8 percent). Axford did struggle with his control (12.6 walk percentage, but that wasn’t his main issue in 2012.
In 139.1 career innings coming into 2012, Axford had given up only five home runs. In 2012, his home run to fly ball rate (HR/FB) ballooned to 19.2 percent (career 8.9 percent, 2012 average: 10.3 percent); he gave up 10 home runs in 2012. Also, Axford could not strand anyone (which could partly be due to the home runs), as his LOB rate dipped to 68.2 percent, much worse than his career or league average.
I think there’s a good chance both of those statistics rebound, and if he can keep the strikeouts up, a bounce-back year could be in store.
2012 numbers: 43.2 IP, 191 BF, 27.8 K%, 4.12 ERA, 100 ERA-
The former Blue Jays reliever’s adjusted ERA was nine percent worse than the average major league reliever in 2012 and the second worst adjusted ERA of his career. Despite these sub-par results and his first stint on the disabled list, Frasor posted the highest strikeout rate of his career. He was especially successful against righties, striking out 35 of the 109 he faced.
Some may look at Frasor’s 2012 season see a guy who is on the wrong side of 30, coming off a career-worst year. But I see a 35-year-old reliever who has had a solid and durable career, and could end up as a free agent bargain, because of his ability to strike out right-handed hitters.
2012 numbers: 66.2 IP, 280 BF, 26.8 K%, 3.78 ERA, 104 ERA-
This was Brach’s first full season in the majors and his unadjusted ERA was close to league average for relievers. But when it was adjusted to take his home park (Petco) into account, it looks much less pretty.
Brach had a surprisingly low BABIP (.245), but I think that was a product of his high walks and high home run totals, which I expect to come down in 2013. He is the kind of hard-throwing, splitter-yielding, high-K guy I think translates to a successful reliever. His services will come very cheap to San Diego next season.
2012 numbers: 70.1 IP, 309 BF, 25.2 K%, 5.37 ERA, 138 ERA-
The Houston Astros right-hander ate innings last year, but his results were just terrible: His adjusted ERA ranked as the 12th worst among relievers (minimum 30 IP). However, Rodriguez throws hard and he had a well above-average K-rate over those innings. Rodriguez struggled slightly with his control, walking 11 percent of batters (league average was just over nine), but I can’t overstate how more important strikeouts are.
Despite his struggles with walks and home runs, Rodriguez’s peripherals (FIP, xFIP, SIERA, etc.) indicate that he was much better last season than his ERA would reflect.
Rodriguez was a solid reliever in 2011 with similar peripherals, but his 2012 strand rate (65.2 percent) caused his ERA to inflate. I think his velocity, strikeouts and peripherals are a better indicator for his future.
Houston could see Rodriguez return to being a very good reliever next year for very little cost: Rodriguez will make the league minimum.
Sample size matters.
The amount of innings that these five pitchers and any other reliever will throw next season will be a small sample. Thus, it’s possibley that all five of these pitchers end up with higher ERAs in 2013.
Strikeouts aren’t everything, but I think given the small sample that relievers’ results are subject to, they give us a much better idea of who could improve, or perform more capably within that sample. Strikeouts hit an all-time high last season around baseball, and relievers like Aroldis Chapman and Craig Kimbrel put up some unheard of numbers.
Given baseball’s current landscape, when it comes to the guys who come out of the ‘pen, it is all about the Ks.
References & Resources
All statistics came courtesy of FanGraphs