There is plenty to talk about the offense. There is also plenty to talk about the bullpen, especially Brad Boxberger and Archie Bradley. Since the All-Star break, the Diamondbacks have blown 8 saves, which is the fifth highest in the MLB. On one hand, the Diamondbacks should be lucky that the Rockies and Dodgers are two of the four teams with more blown saves than Arizona.
On the other hand, this highlights what was a known issue for the team: the back end of the bullpen. Boxberger can be very good - he leads the bullpen in K% and is 17th-best among 154 qualified MLB relievers - but walks and home runs have come back to hurt him on multiple times. Archie Bradley has been great for a year and a half, but it always seemed like it might be a bit of a mirage due to his low walk rates and crazy low BABIPs while not really having a reliable second pitch.
The Diamondbacks seemed to recognize this issue by trading for Matt Andriese, Brad Ziegler, and Jake Diekman but the returns just haven’t been there. Andriese is currently in the minors, Ziegler has an ERA over 5, and Diekman has been decent but only has 7.2 IP since the All-Star Break.
Could the answer to some of the Diamondbacks bullpen woes already be on the team?
The answer is: probably. In fact, there are two of them. However, Yoshihisa Hirano is already getting used extensively as the primary 7th inning guy and is second on the team in medium and high leverage innings, behind only Bradley. One could certainly argue that Hirano should be the team’s closer but that is not the focus of today’s article. Today the focus will be on Andrew Chafin, who in addition to not being high on the bullpen pecking order also seems to not be perceived well by the fanbase.
But are the fanbase’s perceptions of Chafin accurate and/or fair? Let’s find out.
The complaints about Chafin have been heard many times this year. It seems like there are a billion times this season where he has come on to face a batter, walked that batter, then get pulled. This has really shifted the common narrative regarding Chafin to appear very negative. Yet, Chafin leads the Diamondbacks bullpen in ERA and fWAR and is third in bWAR (behind McFarland and tied with Hirano). Maybe there is more to Chafin than what the fans seem to recollect?
To do this, Andrew Chafin is going to compared with Hirano, Bradley, and Boxberger. The splits among all these pitchers are very limited but they’re going to be narrowed to the best “window” to approximate the player’s current talent level (per this author’s subjective analysis):
Hirano: Using 2018 stats only due to only year in the MLB.
Bradley: Using 2017-2018 due to only years as a reliever.
Boxberger: Using 2017-2018 due to health issues prior to 2017.
Chafin: Using 2016-2018 as Chafin made a huge leap from 2015 to 2016 and 2016-2018 seem like similar seasons of output from Chafin.
Feel free to debate the usage of the varying splits here, but they were isolated to pick out the best approximation for the current “true talent level” of each player and the longer time period will only help Chafin’s case.
First, let’s look at 2018 and see which pitchers are used in high and medium leverage innings and their ERAs in said situations:
Diamondbacks High + Medium Leverage IP
|Pitcher||High + Med Leverage IP||High + Med Leverage ERA|
|Pitcher||High + Med Leverage IP||High + Med Leverage ERA|
Bradley and Boxberger have performed the worst among Diamondbacks pitchers in high and medium leverage innings yet get the 1st and 3rd-most innings. This does not mean that they are to continue pitching like this - both Bradley and Boxberger are good pitchers - but it does leave the door open for considering others. Hirano, as mentioned above, has been performing extremely well for the Dbacks and should be considered in a closer or setup role. TJ McFarland has been great this year in a limited sample of higher leverage innings, but his low strikeout rates and high groundball rates push him to more of a Ziegler-esque “fire extinguisher” type of reliever (what is interesting, however, is that TJ’s K% has really spiked in the last 20 games and might be worth keeping an eye on).
Then there’s Andrew Chafin, sitting with barely more innings than TJ and and ERA a full run lower than Boxberger and Bradley. What gives?
It surely isn’t performance related. Using the splits mentioned above, here’s how the bullpen (minus McFarland) compares on overall performance-type stats.
Dbacks Bullpen Comparison
Now this is an interesting chart. Chafin leads the group in FIP by a fairly hefty margin, a large part of which is driven by the fact that he’s been the best at suppressing home runs in this group. Isn’t this something that’s very vital in a high leverage type of situation?
Furthermore, this chart shows that Chafin gets strikeouts at rates very similar to Bradley and Boxberger while not being terrible on the walks, either. Chafin is also the only pitcher among this group with an ERA over his FIP - this is probably partially why the fanbase doesn’t seem to like Chafin much - but most of that is driven by his 2016 season, when he had a 6.75 ERA to a 2.84 FIP (and a .368 BABIP). He’s been on the better side this year, witch his ERA a half run better than his FIP.
Overall, the overall performance seems to support Chafin. But, you can’t talk about relievers without also getting into win probability stuff. FanGraphs doesn’t let you include win probability stats into their Splits Tool, so only 2018 will be analyzed:
Dbacks Bullpen WPA
This chart does an excellent job of showing both why Chafin seems to be disliked and why Chafin should be used more frequently.
While Chafin’s overall WPA is fairly low (largely in part due to his minimal innings in higher leverage), his WPA/LI is right up there with Hirano and Bradley. WPA/LI is context neutral and is better than pure WPA for comparing players as it shows how much value a player added regardless of leverage. Chafin is adding value but has to do it in countless low leverage situations.
The “RE24 Wins” value is another stat that isn’t used very often because it’s not understood very well. RE24 is essentially a “deeper” dive than WPA because it compares the start and finish of each plate appearance relative to the runners on base (if any). It essentially compares the run expectancy that a pitcher adds or subtracts on each plate appearance which also depends on the baserunning situation.
For instance: a runner on 3rd with 1 out has a much greater chance of scoring than a runner on 3rd with 2 outs. If a pitcher gets an out without letting that runner on 3rd score, they are saving more “expected runs” than a pitcher than gets an out with nobody on. That’s what RE24 is calculating and it is a great tool for analyzing relievers.
Anyways, back to Chafin: he’s second best on the team behind only Hirano. Chafin seems to be doing well at keeping runs from scoring, even if you include the one batter walks he’s struggled with.
Speaking of that, let’s talk about Chafin coming in to face single batters. Fifteen times this season, Chafin has come in to face a single batter. He has walked 4 and struck out 3 in those fifteen games while also getting two double plays. He’s given up only 2 hits and 1 run in those fifteen games. That’s really not bad.
If you expand it to games with two batters faced (another 14 games), he’s walked 9 and struck out 8. That’s nearly half of this season’s 20 walks in a span of 43 batters faced. But yet zero more runs.
That’s 10 IP for games with 1 or 2 batters faced with a 0.91 ERA, 7.2 K/9, and 8.1 BB/9.
Meanwhile, if you look at the remaining games (e.g. 3+ batters faced in a game), Chafin has performed much differently. He has struck out 39 batters in 35 IP (10.0 K/9) and walked only 11 (2.83 BB/9) with an ERA of 2.31. The ERA is technically worse, but the overall peripherals are better. But neither situation has been bad for Chafin.
Chafin has performed really well in 2018 and he has a three year body of work that shows that he has excellent underlying peripherals that support his good performance. Chafin seems to have struggles with walks when he comes in the face a specific batter but beyond that, he’s been great. Chafin appears to have done everything to deserve a more significant role in the bullpen and it might be worth making him more of a full inning guy instead of a 1-or-2 batter guy.
Chafin shouldn’t be closer yet, but he seems like an ideal candidate for a 7th or 8th inning guy with more regularity.