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One Big Question: Will we ever see a return of Tyler Thornburg’s stuff?

His return to the mound in 2018 was extremely disappointing.

MLB: Spring Training-Pittsburgh Pirates at Boston Red Sox Jasen Vinlove-USA TODAY Sports

Welcome to Over the Monster’s One Big Question series. For those unfamiliar, this is something of a season roster preview where over the next 40(ish) (week)days we’ll be taking a look at each player on the 40-man roster prior to the season. If changes are made to the roster between now and Opening Day, we’ll cover the newly added players. Rather than previewing what to expect in a general sense, the goal of this series is to find one overarching question for each player heading into the coming season. We’ll go one-by-one alphabetically straight down the roster, and today we talk about Tyler Thornburg.

The Question: Will Tyler Thornburg’s stuff ever come back?

In case you haven’t heard, the Red Sox’ bullpen is a legitimate question mark this season. They are in as good a position to win a championship in 2019 as any other team in baseball, of course, and their lineup as well as their rotation looks to be in fantastic shape. There are a million potential issues that could pop up with the relief corps, and many of them have a pretty decent chance of coming into fruition. For my money, the biggest issue with the group is the trio of right-handed relievers behind Matt Barnes and Ryan Brasier on the depth chart. Specifically, I’m talking about Tyler Thornburg, Heath Hembree and Brandon Workman. They are all out of options, and thus have the inside track on an Opening Day roster spot, and each of them has a low ceiling, a high chance of implosion, or both. In this writer’s humble opinion, though, Thornburg stands out as the biggest concern likely to be on Boston’s active roster on March 28. At the same time, though, based on his major-league track record he has the best chance of the group to step up and be a legitimate late-inning arm.

In many ways, Thornburg is in an extremely similar spot as Carson Smith was in heading into last season. Both were relatively high-profile trade additions and for both the last time we had seen them in a full season with full health they were outstanding. Of course, both of those full seasons were with their previous organizations. For Thornburg, that season was 2016 in Milwaukee, when he transitioned into being a full-time reliever and dominated to the tune of a 2.15 ERA with peripherals to match. Last season, the righty came back and pitched for the Red Sox for the first time, over a year after he was acquired in the Travis Shaw/Mauricio Dubon trade. The results were not good, as he finished with a 5.63 ERA over 24 innings with a FIP that suggests he should have been even worse. He was bad enough that you can’t just point to one issue as the reason behind his struggles. That said, if you had to pick the biggest problem, you’d have to point to his strikeout stuff.

Minnesota Twins v Boston Red Sox Photo by Omar Rawlings/Getty Images

Above all else, that amazing breakout season with the Brewers was propped up by a huge strikeout rate. The righty struck out over 34 percent of his opponents that year, higher than all but seven of the 273 pitchers who tossed at least 60 innings in that 2016 season. He was elite in this area, and it helped mask his below-average control. (His walk rate was 9.5 percent that year.) Fast-forward to 2018 and Thornburg was a totally different guy. Over the small sample size he struck out only 19.6 percent of his opponents. For context, the league-average reliever struck out batters at a 22.3 percent clip in 2018.

Looking a little bit deeper, and it’s no surprise that Thornburg’s plate discipline numbers were significantly worse in 2018 than 2016. According to Baseball Prospectus’ plate discipline numbers his swinging strike rate fell from 28.3 percent in his final year with the Brewers to 20.9 percent last season. All of the increased contact came on pitches in the zone, too, as his Z-Contact rate (contact rate on pitches in the strike zone) jumped by ten percentage points (77 percent to 87 percent). He actually had a slight improvement in contact rate on pitches out of the zone. Getting whiffs on strikes is, in my opinion, the best estimation of a pitcher’s stuff, and Thornburg’s clearly took a significant step back.

Looking at these numbers and seeing the issue was that the issue was on opponents hitting pitches in the zone, a reasonable hypothesis is that Thornburg’s breaking ball wasn’t the issue. The curveball is the righty’s best offering, and it’s generally used to get batters to chase out of the zone. That hypothesis would be correct, as Brooks Baseball indicates his swinging strike rate actually increased on that pitch last year. It was the fastball and changeup that saw major drops, though. The former’s whiff rate fell from 11.8 percent to 5.4 percent while the latter fell from 22.3 percent to 16.9 percent. Unsurprisingly, this correlated with a drop in fastball velocity, which fell from an average of 95 mph in 2016 to 93 mph in 2018. Obviously that hurts the effectiveness of that pitch, but it also limits the effectiveness of his changeup. He went from having almost a 10 mph-difference between the fastball and changeup to a difference of only 8 mph difference last year. It may not seem like a lot, but slight changes here can make big impacts.

Boston Red Sox Photo Day Photo by Elsa/Getty Images

Now, all of this seems bad and the trends lead to some legitimate concern for the coming year. Remembering that Thornburg is attempting to come back from TOS surgery he underwent in 2017, perhaps the most difficult procedure for a pitcher to recover from in today’s game, only makes things worse. If you’re looking for some optimism, hold your hat on the fact that he didn’t get a real spring training last year as he was still recovering from said surgery. This is his first real and healthy offseason since the injury, and the hope is that return to normalcy will help. Early in the spring, the team has done nothing but talk up how strong Thornburg’s stuff has looked. Spring radar guns can be misleading, but the velocity readings we’ve had access to in games have been encouraging. Of course, it hasn’t really helped with the results. The 30-year-old has allowed seven runs in four innings with three strikeouts and two walks.

That brings us back to the point that strikeout stuff isn’t Thornburg’s only issue. He’s allowed hard contact in spring and was hit hard in his 24 innings of work last year. Throw in control issues that have plagued him his entire career, and you get his disastrous 2018. The 2019 season is going to be put up or shut up time for the righty. He’s going to need to limit the damage when batters make contact, but before he gets to that point he simply needs to miss more bats. Once he gets there, it will be easier for the rest to fall into place. Personally, my expectations are low, but if the Red Sox are going to have a late-inning arm beyond the top two that is on the Opening Day roster, Thornburg is their best bet.