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What the Data Says: White Sox Bullpen

This talent-rich group has yet to hit its stride, but still has the potential to be among the league’s best

MLB: Chicago White Sox at Los Angeles Angels
Aside from a couple of bumps, Liam Hendriks has been everything the Sox had hoped for.
Jayne Kamin-Oncea-USA TODAY Sports

What’s happened to the “super pen?”

The White Sox bullpen is currently 13th best in the majors by fWAR. This isn’t something to be worried about yet, but it also doesn’t feel like we’ve witnessed the dominant potential we hoped for when this group was assembled on paper. Some of the 2020 stalwarts have come across struggles early, and Liam Hendriks is below replacement level after 11 innings pitched.

There are certainly more encouraging signs in this piece than worrisome ones, but now with a further injury-depleted lineup, the Sox will need some of this bullpen talent to start performing to the level that they’re capable of.

Liam Hendriks

More than three HR/9, a 71% save conversion rate, and a below-replacement level relief pitcher is not what $18 million was allocated to Hendriks for this winter. However, if you have had any doubts, this is the “don’t panic disclaimer.” That’s right, South Slydah is still filthy.

We’re talking about a 3.86 ERA with a 2.46 xERA. I mean, how in the world did Willie Calhoun make contact with this pitch, much less hit it into the seats?

That’s a 20-inch vertical break (elite), 7.8-inch horizontal break pitch at his head. It’s probably exactly where Hendriks wanted it.

The fastball movement is still there, the velocity is actually up a tick, and its Whiff% is up 2%, a pitch he’s now using 7% more than last season. Hendriks has also been more efficient at the top of the zone, and thus we’ve seen an even flatter vertical approach angle. Getting on plane with an elevated Hendriks fastball is usually a tall task, but Calhoun didn’t get the memo.

Earlier this year, I theorized that perhaps Hendriks should use his curveball more often this year. This was because according to my pitch tunneling metric as a part of xRV 2.0, Hendriks’ curveball was the best tunneled pitch in baseball last season. He creates an almost perfect spin mirror, with a ton of backspin on his fastball and a ton of top-spin on his curve. The problem was, Hendriks only threw 26 curveballs (7% usage). This year, he hasn’t bumped up that usage, and it looks like he’s struggled to command it. I still think there’s room for him to take advantage of his fastball/curveball relationship more.

Even though he’s decreased his slider usage by 7%, it’s still Hendriks’ breaking ball of choice. The pitch is characterized as a slider, it’s really shaped like a cutter now thrown at 88 mph with a 165-degree spin axis. It’s still generating more than a 50% whiff rate, and he typically buries it low and away to right-handed hitters.

Hendriks absolutely is still going to be an elite closer. Heck, his fastball is so good that hitters can know it’s coming more than three quarters of the time and they’re still hitting .200 against it. The most disappointing thing is that it doesn’t look like Tony La Russa will use Hendriks creatively, like I had hoped. Maximizing his marginal impact on the game, whether that be in the seventh inning or the ninth inning, should be TLR’s goal. But I digress ...

Garrett Crochet


OK, calm down.

After averaging 100 mph on his heater in 2020, Crochet has yet to hit the century mark this year. He maxed out at a measly 98.9 mph in Los Angeles to start the season, and he is currently averaging 96.3 mph. While I will concede that any time a pitcher drops more than 3.5 mph on his average fastball it should raise some red flags, expressing the sentiment that Garrett Crochet at 95-98 mph “simply won’t work” is complete blasphemy.

What Crochet did last season was set an incredibly high bar for himself moving into his first full season. He was never going to be able to sit in the triple digits. I’ve also seen others speculate that he’s not entirely healthy (prior to the upper back strain that landed him on the IL) after a scary forearm strain ended his 2020 season in the Wild Card round — an injury that I (and many others) felt that meant Tommy John surgery was in the cards. However, if Crochet was not 100% in any fashion, I can guarantee he wouldn’t have been pitching. One of the big reasons that has been in the major league bullpen and not developing as a starter in Birmingham is that he’s on an innings limit in 2021. After only a handful of innings in Knoxville plus six for the White Sox last season, the club is forced to be careful.

It took Crochet fewer than 100 pitches last year to wind up with a left-arm injury by throwing in a way that wasn’t sustainable health-wise long-term. Staying healthy, improving his fastball command and developing his slider and changeup were the main focuses of smoothening out his delivery — an effort that both Tony La Russa and Rick Hahn have alluded to. Once Crochet hones in on a cleaner path down the mound, it’s my guess that he’ll start sitting in the upper 90s again.

The velo dip hasn’t come without coinciding positive “stuff” developments. Crochet’s fastball vertical break is up 2.6 inches to 18.5, a big factor that has helped to offset less velocity. Although, he hasn’t exactly located the pitch according to its strengths: Too many have been center-cut or at the bottom of the zone. With Crochet’s velocity, vertical movement, and deceptive delivery, he should be looking to elevate.

Here’s an example from last Sunday afternoon’s game where Collins wanted him to elevate for a punch-out, but Crochet couldn’t hit his spot. Notice Collins’ setup pre-pitch. He should be getting more that 20% whiffs on his heater, and misses like this one are why he’s not.

Crochet is currently running a 60% ground ball rate, which isn’t exactly expected from an 18-inch+ vertical break fastball-pitcher. However, when you consider that Crochet is releasing the ball seven feet from the mound (which is very close to the hitter, relatively) and six and a half feet above the ground (which is very high) he’s basically shoving his fastball down the throat of hitters. This works to create a steep -5.4-degree vertical approach angle, helping to somewhat explain the abundance of ground balls. Still, molding the next Dallas Keuchel isn’t the goal here.

The movement on Crochet’s slider has become lethal. He’s creating almost nine more inches of drop and four inches of horizontal break compared to last year (albeit, we only saw eight of them). The pitch now has 82nd percentile vertical break and 96th percentile horizontal break vs. the average slider at 83 mph. His command of it hasn’t been lethal, however. It’s the only reason he’s given up a couple of knocks on it so far and only has a 28% Put Away rate.

Let’s hope this IL stint is a brief one.

Codi Heuer

Heuer, one of the most pleasant surprises of the 2020 season, has run into somewhat of a sophomore slump this year. He is getting hit hard. His biggest issue has been his sinker that currently holds a .470 xwOBA and a .471 batting average against. The above average velocity (97-98 mph) from his deceptive motion is still there, and so is the movement by and large. What’s changed is his location of it. Last season, Heuer was extremely effective at letting his sinker run arm-side — away from lefties and in on the hands to righties. This year, many lefties have seen sinkers from Heuer than start in and off the plate before the pitch runs over the late to meet their barrels. They alone have a .593 xwOBA and are slugging 1.188 against it. This very reason is why we sometimes see sinker-heavy right-handed pitchers opt for a four-seamer against lefties.

Here are a couple examples from Sunday’s rough outing:

What’s interesting, and also troubling, is that it looks like Collins wanted both of those pitches on the inner half. What we need is more of these, from last year:

You can see McCann set up middle away for Heuer’s aiming point. From there, you just let his impact horizontal break take care of the rest. The only whiffs Heuer has gotten on his sinker this season have been when he gets it elevated to the top of the zone.

Both of Heuer’s secondaries been viable, though his slider has gotten slightly worse results while the changeup has been better. He’s really gotten on top of his slider more, creating more backspin to give the pitch even more of a cutter profile than the one he had last year. His slider’s spin axis has gone from 151 degrees last year to 171 degrees now. I would love to see Heuer try to revert to the slider shape of last season (or even closer to a traditional slider of 90 degrees) in an attempt to get its whiff rate back to where it was at 67%. It’s down to 41% now. Heuer’s slider was in the 67th percentile of pitch tunneling (with his sinker) last year from my tunnel metric, and before seeing 2021’s results, I’m willing to bet that it hasn’t worked as well this year.

Even though Heuer set himself a pretty high bar after successful rookie season, he still has the ability to return to that back-end form that we saw. That .474 BABIP ain’t staying around for long. His changeup being a usable third pitch can set him apart from other hard-throwing relievers with only a good two-pitch combo. Bumping up its usage could be a potential solution for neutralizing lefties.

Aaron Bummer

There’s no way Aaron Bummer can be fun to face. You’ve got limbs flyin’ around and a guy slingin’ an upper-90s sinker and devastating slider across his body.

That sinker/slider combo features ridiculous movement. His sinker gets 99th percentile vertical movement vs. average. In other words, only Minnesota’s Randy Dobnak gets more. It also gets 63rd percentile horizontal run.

Yeah, nasty. Except it’s getting hit a lot harder this year. It had a .364 BA and a .342 xwOBA (51st percentile) compared to a .200 BA and a .254 xwOBA (97th percentile) in his breakout 2019 season. It shouldn’t be getting hit to the tune of an average sinker, especially with it also being 96 mph on average and with the kind of slider Bummer has in his back pocket.

Bummer’s slider gets the seventh-most vertical break (drop) vs. average, and the second-most horizontal break, only behind the Angels’ Shohei Ohtani. With that kind of movement, it gets the kind of results you’d expect — it has a .089 xwOBA and a 62.5% whiff rate. Bummer traded in his average cutter for this sensational masterpiece of a breaker. At only 16.2% usage, one could even argue that Bummer should throw more sliders given the present command struggles with his sinker — which brings me to Bummer’s overarching issue.

Through the first month of the season, Bummer has a sixth percentile first-pitch strike rate (47.6%). His great stuff can’t play the way it’s designed to when he’s constantly behind in the count. In 2019, Bummer’s F-Strike% was 59%. Trusting the pitch’s movement and hitter’s propensity to beat it into the ground is likely the key focus point moving forward, but maybe more sliders instead of cutters and some of the sinkers is 1A.

Evan Marshall

Ever since Marshall started throwing his changeup more often than not, his career has completely changed. At the beginning of last season, I talked about the changes Marshall has made to revive his career, for South Side Hit Pen. An xRV darling, Marshall’s changeup was once again among the league-best pitch types as it ranked in the 97th percentile overall last season.

Marshall’s ability to not only generate above average total movement on the pitch, but also live on the corners of the zone is what has made him so effective over the past couple of seasons. His 49% Edge% ranks in the 94th percentile, a metric that Marshall has been in the 90th percentile or better since 2019.

As far as 2021 is concerned, Marshall has run into some tough luck. He has a .352 wOBA with a .281 xwOBA and a 6.54 ERA with a .298 xERA. His changeup alone has a .509 wOBA vs. a .307 xwOBA. The pitch location height on that changeup has began to creep up, and that’s not what Evan or any of us want.

The most puzzling result of all for Marshall has been his curveball’s performance. It was his best pitch by xwOBA (.110), and hitters only had a .056 batting average against it last year. It has a .225 xwOBA this year which is still great. Marshall also had a 58.5 % whiff rate on his curveball in 2020, as perfectly mirrored spin axis with his changeup and four-seamer created great deception. Only Blake Snell and Liam Hendriks had better curveball whiff rates. This year? Marshall hasn’t generated a SINGLE WHIFF on his curveball through 42 pitches.

The movement is still there, the stuff is still there and Marshall is still using his curveball to complement his same changeup and fastball. Thus, I am going to chalk this one up to early season weirdness. That’s right — stay tuned for an Evan Marshall curveball whiff coming soon (and hopefully fewer barrels).

Matt Foster

When the White Sox protected Matt Foster from the Rule 5 draft prior to last season, I can say I was asking, “why?” Then Foster was brought to the majors promptly, featuring an 18-inch+ vertical break four-seamer and a changeup that played very nicely off of it, and my question was quickly answered.

Foster’s 2020 fastball was in the 76th percentile by Expected Run Value (xRV) as it tunneled nicely (75th percentile by my tunnel metric) with his changeup and slider. Now in 2021, Foster’s fastball velocity is up slightly and his vertical break is up 1.3 inches (a considerable jump) to 19.4 inches. He traded some of his horizontal break for vertical, and especially for Foster’s profile, it should end up being worthwhile. Vertical break is great for whiffs, and Foster has generated a lot more of them this year.

At 38.8% whiffs, Foster ranks in the 95th percentile, up from a solid 75th percentile a year ago. That improved fastball has generated 8% more whiffs on its own. His changeup, a pitch that gets way below-average total movement, is also getting 10% more whiffs. The pitch works due to its relationship with his fastball; there’s only about a 20-degree difference in spin axis between pitches, and Foster has gotten it down around the knees much better this year.

But have these changes actually been worthwhile so far? That ugly 9.71 ERA begs to differ. While we obviously care about more that just earned run average (especially for relievers), Foster’s xERA is still only in the 42nd percentile at 4.22. The killer was that dreadful April 7 outing against Seattle, where Foster blew the White Sox lead en route to an 8-4 loss. In just two-thirds of an inning, Foster gave up five earned on five hits. But how bad was Foster on ths in reality?

Here’s the location of each of the five hits. I don’t know if any of these five pitches were not executed to Foster and Grandal’s design.


The in-zone changeup was a base hit for Taylor Trammell on an 0-0 count. Belt-high changeups usually aren’t good, but a rookie swatting one for a first-pitch base knock? Credit Trammell.

How about this garbage?

Not a lot can be said, it’s just brutal luck.

Also in the inning, Jose Marmolejos yanked a pitch at his eyes (the highest fastball in the above chart) into right-center for a 100 mph base hit against a 20-inch vertical break heater at 95 mph. The batted ball had a .920 xBA. Again, Foster executed, but the hitter executed better.

The point here is that Foster still looks like a solid middle reliever in this bullpen — his outlook hasn’t changed. He has a 3.00 ERA and a 2.58 xFIP since that outing in Seattle. THE BAT, a projection system that takes Statcast data into account, projects the rest of Foster’s season at a 3.45 ERA and 10.5 strikeouts to 2.7 walks per nine innings. It also projects a normalized BABIP nearly 60-points lower than where it currently sits.

José Ruiz

The 2021 season has been (and will continue to be) do-or-die time for Jose Ruiz. Out of options, he’s been surprisingly impressive through 11 13 low-leverage innings pitched.

Aside from a four-seamer with solid ride, Ruiz’s stuff is pretty meh, and by “meh” I mean his four-seam’s vertical break is the only above-average movement he gets on any of his four offerings, with the others not being particularly close.

All said, even with that stuff paired with seemingly average command, Ruiz is sitting in the 88th percentile for xwOBA and the 84th percentile for barrels. Both his fastball and slider whiff rates are up, with batters only hitting .050 on the former. So however he’s doing what he’s doing, he should keep doing it.

And that’s about it. If you came here for an extensive José Ruiz breakdown, I apologize. There just isn’t that much to like here. How he’s starved off getting pummeled to date may be a story in itself. Once Crochet and Jace Fry are back in the fold, a newcomer like Alex McRae potentially looks to have more upside, or Ruiz inevitably starts to struggle sooner rather than later, the converted catcher may be on the DFA train as that .143 BABIP regresses towards the mean. Options like Zack Burdi, Tyler Johnson, Jimmy Lambert or even Reynaldo López would likely be next up.

Not to be callous towards Ruiz — he’s done his job so far, but we have a fairly large sample size from him dating back to 2018 where he’s pitched to a 5.36 xFIP.

*Note: Michael Kopech was included in the starting pitcher’s section of this analysis