Depending on what numbers you’re looking at, you could have two very different impressions of Jake Diekman. He turned 35 years old in January, and he’s coming off a season with the worst home run rate and FIP of his career. On the other hand, his strikeout rate remains elite, his ERA was the lowest it’s been in a full season since 2016, and his four-seamer is as fast as ever.
So, what can we expect from Diekman in 2022?
Age Is Just a Number?
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On March 16, Jake Diekman signed with the Boston Red Sox for two years and $8 million.
Only one pitcher older than Diekman signed for more guaranteed money – Mark Melancon, who signed with the Diamondbacks for two years and $14 million. Diekman turned 35 this past January, while Melancon will turn 37 at the end of March.
35 is an age that can set off alarm bells in a baseball fan’s head, and not without reason. The league average ERA last season for relievers aged 30-34 was 3.80, while for relievers 35 and over it was 4.53. Pitchers 35 and older accounted for just 7.2% of all innings pitched in 2021.
However, while 35 may be an age at which many pitchers start to decline, it is certainly not an age at which decline is inevitable. Several relievers over 35 found success last year, including Melancon, Craig Stammen, and Steve Cishek.
And although age can be a cause for concern, experience can be one of a pitcher’s greatest assets. Since Diekman’s first qualifying season in 2014, only two relievers have pitched more qualified seasons: Kenley Jansen and Tony Watson.
So, while it’s understandable to feel hesitant about giving a multi-year deal to a pitcher born during the Reagan administration, we have to look beyond just Diekman’s age to project how he’ll perform going forward.
The Best of WAR, the Worst of WAR
Jake Diekman’s age is not the only number that makes him hard to predict. According to the RosterResource Free Agent Tracker on FanGraphs, Diekman has the third-highest projected WAR of all relievers who were available this offseason, and the highest projected WAR among relievers signed since the lockout ended. And yet he is also the only reliever to sign a multi-year deal this offseason who had a negative fWAR in 2021. No reliever with a negative fWAR signed for more guaranteed money either.
WAR is not a great metric for evaluating relievers, because they pitch so few innings and because WAR has a pretty sizeable margin of error. However, WAR is still useful for getting a general sense of how well a player performed in one season and how he can be expected to perform going forward.
This means that the discrepancy between Diekman’s 2021 WAR and his projected 2022 WAR isn’t necessarily a big deal, but it points to Diekman as the kind of player worthy of a closer look.
Highest Home Run Rate of His Career
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The four main components of FanGraphs WAR are strikeouts, walks, home runs, and innings pitched.
As you can see, Diekman’s high 1.48 HR/9 is the real cause for concern here. His previous career-high in a full season was nearly half that – just 0.77.
Even looking beyond just these few statistics, Diekman’s home run rate remains the one number that really stands out. Thus, whether he succeeds or fails with the Red Sox hinges on his ability to prevent balls from leaving the park.
This is some of Diekman’s batted ball data from 2021 compared to his career averages.
His high home run to fly ball ratio is a good sign. Typically, over a large enough sample of batters faced, a pitcher’s HR/FB can be expected to regress towards his career average, which means that it is unlikely Diekman will continue to allow home runs on 16.4% of his fly balls going forward.
However, that doesn’t mean that Diekman’s high home run rate in 2021 was just a fluke. As you can see, his average launch angle allowed was higher than it’s ever been, and his fly ball rate was well above his career average. Thus, not only were more of his fly balls going for home runs, but he was allowing far more fly balls in the first place.
They weren’t cheap fly balls either. His average exit velocity was more than two MPH faster than his career average. For context, that difference in exit velo is the same as the difference between 2021 John Means (87.9 MPH, 71st percentile) and 2021 Erick Fedde (90 MPH, 25th percentile).
As a result of Diekman’s high launch angle and exit velocity, his barrel rate was nearly twice his career average. In fact, according to FanGraphs, he allowed as many barrelled balls in 2021 as he did from 2017-2020 combined.
This should be concerning to Red Sox fans, no doubt about it. Diekman allowed a lot of quality contact in 2021, which is exactly what a pitcher doesn’t want to do. And yet, that barrel rate is such a big jump up from his career average that I would take it with a grain of salt. Maybe some freshly cracked pepper too.
The Meatball of It All
Why is it that Jake Diekman allowed so many more barrels in 2021 than ever before? One possible explanation is that batters were swinging at his mistake pitches more often than they usually do.
Baseball Savant has a fun statistic called “Meatball %”, which keeps track of how many pitches a pitcher has thrown straight down the middle of the plate. Savant also keeps track of “Meatball Swing %”, which tracks how often batters were actually swinging at those meatball pitches.
Diekman’s 2021 meatball swing rate stands out from his other plate discipline numbers on Savant.
He wasn’t throwing meatballs any more often than usual, but hitters were swinging at his meatballs far more often than ever before. And unsurprisingly, pitches that Diekman threw right down the center of the plate were more likely to be barrelled and more likely to be home runs than pitches that he threw anywhere else.
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There’s still only so much we can glean from this small sample of data. Meatballs only accounted for 80 of the 1118 pitches Diekman threw last year, and even 1118 pitches is a small sample size. We know that Diekman was punished more harshly for his mistakes than usual, but it’s hard to say for sure if that was simply bad luck or if – for some reason – his meatballs were easier to hit in 2021. We’ll just have to wait and see what happens in 2022.
Benefits of a Small Sample Size
Jake Diekman allowed 10 home runs in 60.2 IP last season, and that’s considered a small sample size because it’s hard to draw generalizations from that amount of data.
However, one benefit of small sample size is that it’s much easier to dive into the details. If you can’t generalize, why not get super specific instead? For instance, we can look at all 1o homers Diekman allowed in 2021 and search for any notable patterns.
The most obvious pattern is the handedness of the batters. Diekman, who is left-handed, has actually been quite good against right-handers throughout most of his career. However, there is a chance that, as he is aging, Diekman will become more and more of a lefty specialist. It’s something for the Red Sox to keep an eye on.
Another thing that immediately stands out from this data is that we’re looking at a strong group of power hitters (Andrelton Simmons and Donovan Solano aside). These hitters combined for a 20.2% HR/FB last year, while the league average was just 13.6%. Combined, these guys hit 262 home runs* in 2021 – the same amount as hit by the MLB-leading Blue Jays. (*Mitch Haniger’s home runs were counted twice, because he hit two homers against Diekman.)
Obviously, every pitcher has to face good hitters (and high-leverage relievers even more so), but it’s still worth pointing out that Diekman wasn’t giving up all those home runs to just anybody.
Another thing that stands out is the ballparks where Diekman allowed these home runs. Of the 10 home runs, only one came in a home run-friendly ballpark – Teoscar Hernández’s homer at the Rogers Centre in Toronto.
There are two ways to interpret this. On the one hand, it’s worrisome that Diekman allowed so many home runs in pitcher-friendly parks. But on the other hand, it’s a great sign that he was able to keep the ball in the yard in hitter-friendly parks.
Using the Park Factors available on Baseball Savant, I counted up how many innings Diekman pitched last year in “home run friendly” stadiums (the top 15 stadiums by HR factor) and “home run unfriendly” stadiums (the bottom 15 by HR factor). Funnily enough, when he was on the road, Diekman pitched exactly 17.1 innings in each. He allowed 3.12 HR/9 in the home run unfriendly parks, and 0.52 HR/9 in the home run friendly ones – exactly the opposite of what you’d expect.
Ultimately, I think it’s a good sign that Diekman was able to limit home runs in the tougher stadiums. If he was truly declining, I’m not sure we would see that pattern.
Park-Adjusted Metrics
Jake Diekman performed much better according to park-adjusted metrics than non-adjusted stats.
As I mentioned earlier, Diekman’s FIP was poor in 2021. But his cFIP – which is akin to FIP but which adjusts for the effect of specific batters, stadiums, and more – was actually 7% above league average. Similarly, his DRA – which is like runs allowed per nine innings, but which also adjusts for factors like quality of opponent and ballpark – was 14% better than league average.
These numbers support the theory that, perhaps, the positives of Diekman’s strong performance in hitter-friendly stadiums outweigh the negatives of his failures in pitcher-friendly stadiums.
In Conclusion
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It’s fair to be a little concerned about Jake Diekman. He’s reaching an age where pitchers get less and less effective, and the amount of home runs and barrelled balls he allowed last year is worrisome. But after taking a detailed look at his 2021 season, I think he’ll be just fine.
He struggled against righties, but he was as good as ever against lefties. He struggled on the road, but he was as good as ever at home. And while he struggled in certain ballparks, he flourished in others.
The Red Sox might be wise to limit Jake Diekman’s appearances against right-handed hitters, but he should do well in the “home run unfriendly” confines of Fenway Park, and there is little reason to believe that his physical decline is imminent.
Photos by Wikimedia Commons | Adapted by Doug Carlin (@Bdougals on Twitter)