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Spencer Turnbull’s early season success holds up to scrutiny

He may be over-performing, but Turnbull has earned his hot start.

Cleveland Indians v Detroit Tigers Photo by Gregory Shamus/Getty Images

On every young player’s trajectory to the major leagues, expectations will color perception. If Spencer Turnbull had entered the 2019 season as one of the top pitching prospects in baseball, you’d probably be hearing and reading a lot about him nationally. Instead, what the Tigers appear to have in the 26-year-old right-hander, is a late bloomer catching people by surprise, and perhaps a pretty good one.

That isn’t to say that Turnbull didn’t have some pedigree. He was a late second round pick by the Detroit Tigers in the 2014 amateur draft. His junior season he was the ace for the University of Alabama, pitching in one of the better baseball conferences. He had the ideal build for a durable hard-throwing starter, and from the beginning he packed a standout fastball. Turnbull was ranked as the Tigers’ fifth best prospect in 2015 by MLB Pipeline, though only Michael Fulmer placed in the overall top 100.

So he was viewed as a decent pitching prospect, but not one to dream wildly about. After a nice full season debut in 2015, he had shoulder issues in 2016, and minor flareups the next two seasons. An improving farm system and Turnbull’s stall in development saw him sliding down rankings of the Tigers’ farms system.

In 2017, he got some consistent innings under belt and finished the season with his Double-A debut, and that was when Turnbull started to gather some momentum as his control and secondary pitches improved. Last season he threw 135 innings, crossing five levels of the farm system from a brief rehab assignment in rookie ball all the way to the major leagues. The ability to pitch regularly for two seasons began to pay dividends in his control, and his slider improved substantially as the year went on.

The line on Spencer Turnbull has always been that he would make a solid back-end starter if he had the durability to eat innings and otherwise might make a good late innings reliever who could cut loose for short bouts of high-90s velocity. But so far in 2019, he has looked a lot like the mid-rotation starter that most saw as his absolute best outcome as a prospect. And, there are signs to indicate he may be here to stay.

Spencer Turnbull 2017-2019

Season IP ERA FIP K% BB% HR/9
Season IP ERA FIP K% BB% HR/9
2017 (A+) 82.2 3.05 3.36 19.4 7.6 0.33
2017 (AA) 20.1 6.2 3.32 23.7 8.6 0.44
2018 (AA) 98.2 4.47 3.16 24.9 9.5 0.36
2018 (AAA) 13.1 2.03 1.38 35.9 5.7 0.00
2018 16.1 6.06 2.85 21.7 5.8 0.55
2019 44.2 2.42 3.63 23.0 9.4 0.60

Even a cursory reading of his numbers should impress. Turnbull has only made eight starts, so we’re going to have to go deeper than just his FIP components to consider how sustainable this success is, but his 2.42 ERA—ninth best in the major leagues—is fairly well supported. We’re not going to start the Cy Young campaign just yet, but the underlying fundamentals are solid enough to suggest that he’s not going to fall apart, either.

Turnbull’s strikeout-to-walk ratio is respectable, which was always the basic concern for him in the minor leagues prior to his 2018 breakout. And where he’s really shined is in limiting home runs. As xFIP tells us, with a league average home run rate, Turnbull would look like a league average starting pitcher with a 4.46 ERA. That would be fine, of course. Few were expecting Turnbull to hold down a spot in the rotation this year to begin with. But Turnbull has a long history of suppressing home runs, and there are good reasons to believe he can keep the long ball from catching up to him this season.


Even back in his college days, Turnbull would touch 98 mph with life, so he wasn’t flying under the radar when he went 63rd overall in the draft. The issue was always his control, and lackluster strikeout ability for a college pitcher in the minors. While his control has improved, he’s still not going to impress with his precision at the major league level. Where things changed in late 2017 and in 2018 was in the consistency of his swing-and-miss stuff. Turnbull refined a quality slider, and the curveball which seemed to go dormant for long stretches of his minor league career began looking like a more potent weapon with tight spin and good velocity. Neither is quite a plus breaking ball, but paired with his fastball, they’re certainly good enough.

So far in 2019, Turnbull’s underlying marks, such as his O-Swing—how often hitters swing at pitches out of the strike zone—and his swinging strike rate, are both basically league average at 30 percent and 11 percent respectively. They suggest Turnbull deserves a roughly average strikeout rate, and that’s how it’s played out on the field so far. There’s really nothing, other than the potential that hitters get used to seeing him and adjust, to suggest he can’t sustain his average strikeout numbers thus far.

Suppressing home runs

Here is where Spencer Turnbull is particularly interesting. There are only four qualified starters in the major leagues who have thrown a higher percentage of fastballs. Turnbull is leaning on his fourseam-sinker combination quite a lot, throwing 65.3 percent fastballs, and yet only 23 of 169 pitchers (min. 50 results) have lower isolated power marks (ISO) against the fastball than Turnbull’s .109 mark. He’s pumping a lot of heaters in there and hitters aren’t exactly baffled about what’s coming next, but so far he hasn’t been hit for much power at all, allowing just two home runs.

The reason we’re focusing on the fastball, is that throwing a fastball that doesn’t get hit hard too often is one of the key facets of a pitcher’s success in an era of hot baseballs and launch angle tuned swings. Pitchers with great fastballs have continued to succeed despite heavy fastball usage. Pitchers without one, have had to scramble to find a way to use the fastball effectively without taking major damage. Many have largely turned to deceptions such as hiding the ball longer in their delivery, or trying to play with hitters’ timing. Others, have simply had to lower the amount of fastballs in their pitch mix. None of these options are easily implemented without cost to their strike throwing and to the rest of their repertoire.

The wrinkle that Turnbull has on hitters, is that not only does he have good velocity and life on the fastball, but he actually mixes two pretty distinct fastballs. One is a fourseamer that doesn’t really ride as much as you’d like and is fairly straight. He’ll even turn it into a true cut fastball on occasion, though rarely. The other, which he uses a little more judiciously, is a sinker that does have some quality sink, but also runs hard toward a right-handed hitter. Because he mixes them up effectively, hitters have a hard time anticipating which fastball is coming and can’t easily accustom themselves and anticipate the life on the pitch. As a result, Turnbull has been able to keep the ball off the barrel of opposing bats.

All three home runs Turnbull has allowed this year have to been to left-handed hitters, which is another thing to keep an eye on going forward. He’s throwing his changeup even less this season, and he may end up needing that pitch to keep lefties in check as the season progresses.

But let’s stick to the fastball for the moment. Here’s the results of Turnbull’s fastballs this season so far.

Things do look different if we overlay Turnbull’s fastball spray chart onto a home-run friendly park such as Guaranteed Rate Field, home of the Chicago White Sox. There are a few more loud outs, and two doubles in particular, that could’ve gone for home runs. As we get to the summer months, and the baseball starts flying a little further, there is probably some trouble brewing in this facet of Turnbull’s game.

Throughout his career in the minors, Spencer Turnbull kept a stranglehold on opposing home run power. He’s going to need to maintain some of that ability that if he’s going to hold up as an above average starting pitcher. Odds are, that isn’t going to happen entirely as the weather warms and hitters get a little more familiar with his twin fastball approach. However, as long as he can continue to keep the walks under control, the crash should be modest. Expect Turnbull to have some games where he gives up bombs at the wrong time, but the versatility of his fastball, and high groundball rate is still going to be there to get him out of jams and take advantage of the Tigers improving defensive positioning.

In the end, the Tigers probably haven’t developed a high quality 2-3 starter here. We’re early in the season, and Turnbull has a lot to prove. But overall, I think we can remain confident that even as corrections occur, Turnbull’s floor now looks higher than it once did. Spencer Turnbull looks good enough to pitch in a major league rotation for years to come. It’s just that he’s probably much closer to just a league average pitcher than his early results might lead one to believe. Considering most still expected him to top out as a reliever or as starting pitching depth as recently as last year, that will do just fine.