Welcome to our surprising starts series. Every week we’ll be going over a few surprising starting pitcher performances around the majors to determine whether these starts were smoke and mirrors or something more.

This week we saw the promotion of a big time pitching prospect, an unheralded spot starter come up big for the Cubs, and Wei-Yin Chen take his home/road splits to a new extreme.

Michael Kopech's debut was cut short by rain on Tuesday, but that's okay since he held the Tigers to one run next time out on Sunday. Alec Mills made the most of a spot start by striking out eight Reds and extending his stay in the rotation, while Wei-Yin Chen had his first double digit strikeout game in over two years.

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Alec Mills, Chicago Cubs

2018 Stats (Triple-A): 124.2 IP, 4.84 ERA, 4.20 FIP, 2.63 K/BB ratio

08/24 vs. CIN: 5.2 IP, 3 H, 1 ER, 1 BB, 8 K

Mills made a spot start on Friday, his first MLB start, and had the Reds flailing at his pitches for a dominant performance. Mills isn’t exactly a household name, though Royals fans may remember his three inning, five earned run stint with the club back in 2016. Probably not, but it would be nice to know that someone knew who Mills was before this start. He actually had a little prospect with the Royals, and Eric Longenhagen of FanGraphs ranked him as the tenth best prospect in the Cubs’ system last fall. That says more about the Cubs’ farm system then it does about Mills, but it proves he wasn’t a total unknown before this start. He performed well in the low minors and at Double-A, but Mills never adapted to Triple-A. He has a 4.53 ERA and 2.68 K/BB ratio in 196.2 innings at Triple-A all-time. That’s even more scary considering he was old for the level at every stop.

Mills has a five pitch repertoire: a 90 MPH four-seamer and 90 MPH two-seamer, a changeup, a slider, and a curveball. He managed six swinging strikes between his two fastballs, a remarkable feat given its poor velocity. He also got five of his 14 swinging strikes with his slider on just 15 pitches. Mills doesn’t have the strongest pitch arsenal, but the slider was the standout pitch in this game.

Mills has a slow slider, clocking in at 78 MPH on average. It looks more like a curveball than a slider at times, and that’s because of its big, looping side-to-side action and high spin rate. Mills’ slider averages 2621 RPM, near the high-end of sliders in the majors and a higher spin rate than his curveball. Here’s an example of one from this start.

Definitely not a hard, down in the dirt slider; Mills doesn’t have the ability to that. Not only is the pitch a little slower and loopier than the average slider, Mills uses it oddly. He threw a first-pitch slider to right-handed batters 50% of the time in this start. He pitches backward, throwing slider fist and using his sinker 40% of the time with two strikes. It’s an interesting approach to take, but for a pitcher with low velocity Mills may do this to keep hitters off balance.

While one could call Mills resourceful, it’s hard to see longevity in this approach. He had 5.1 career major league innings prior to this game, so major league teams are wholly unfamiliar with Mills. Rookie pitchers can often get by on deception for their first few starts before opponents find a way to counter him. The slider is an interesting offering, but the fact that Mills had a 7.7 K/9 at Triple-A speaks to the limitations of his repertoire. The fact that he got so many strikeouts and whiffs with his fastball is most likely the result of both deception and a weak opposing lineup. The Reds were without Joey Votto and Scott Schebler in this one, making Eugenio Suarez and Scooter Gennett the only two fearsome opposing hitters. This start was surprising and impressive, however there isn’t much to build on here.

Verdict:

Mills stifled a watered-down Reds lineup by pitching backwards and using deception rather than overpowering hitters. The slider is his best pitch, but the fastball performance in this start looks unsustainable. Poor Triple-A numbers don’t portend good production. Mike Montgomery will return soon, meaning Mills may only have one start left in him. It’ll come Wednesday against the Mets at home. He is usable in that matchup as a one-off streamer, but certainly not a must add.

Wei-Yin Chen, Miami Marlins

2018 Stats (prior to this start): 100.1 IP, 5.20 ERA, 5.03 FIP, 2.0 K/BB ratio

08/25 vs. ATL: 6 IP, 6 H, 0 ER, 2 BB, 10 K

Where did this come from? This was Chen’s first double digit strikeout game since May 11, 2016 and only the third of his career. He got a whopping 15 swinging strikes, including 13 with his fastball. The most notable thing about Chen’s season thus far had been his massive home/road splits. After this start he has a 1.86 ERA at home and a 9.35 ERA on the road. Are we supposed to believe he is a Cy Young contender pitching at Marlins Park and an utter dumpster fire on the road? It’s so bad that the Marlins are making a concerted effort to pitch Chen at home as much as possible, shuffling their rotation around when necessary. It’s worked thus far, as Chen has a 1.54 ERA in four starts in August, with three of those starts coming at home. He’s had enough success that Chen can’t merely be written off anymore.

Not much has changed in Chen’s pitch mix. He is still throwing a 91 MPH four-seamer, a slider, a curveball, and a changeup. There are two minor changes, in that he is throwing his slider more than ever, and he has eradicated his awful two-seamer from his arsenal. Slider usage is up about 5% from Chen’s career average, and that is a good thing, since the slider has proven to be Chen’s best pitch. It has a .240 BA and .417 SLG against, but xStats suggest the pitch could be even better. Batters have a .204 xBA and .240 xwOBA against Chen’s slider, and the average exit velocity against is a mere 85 MPH. The slider may only have a 9% SwStr rate, but a 49% groundball rate coupled with low exit velocity means lots of easy groundball outs.

That leads us to the bigger issue. Chen is no fireballer and has always been a little lacking in the strikeout department. Including this game he has a 7.19 K/9 on the year, so the ten strikeouts were truly an anomaly. One thing that is immediately noticeable upon re-watching Chen’s outing is the amount of high heat he was dishing out. With some pitchers the high fastball has shown to be as effective as a good breaking ball for whiffs, notably J.A. Happ. Chen isn’t about to become the next J.A. Happ (despite them both being mid-thirties lefties with below average velocity), but he may have tapped into something in this start. Here is a heatmap of Chen’s fastball location from this start.

And here’s his season-long fastball location, excluding his most recent start.

It got plenty of whiffs too, as Chen piled up 13 swinging strikes with his fastball. Many of them came from the high fastball. Here’s a heatmap of fastball whiffs based on location from his start against the Braves.

This mostly makes sense, but why are hitters missing a 91 MPH fastball right down the middle. Either Chen had some crazy deception going on, or some really poor hitters swung at those pitches. Three of his 10 strikeouts came against opposing pitcher Anibal Sanchez, and Sanchez accounted for two of those middle of the zone whiffs as well as one towards the top of the zone.

This big strikeout total seems like the confluence of a few things: a new approach from Chen, taking advantage of weak hitters, and an off night from the Braves. It’s hard to say if Chen will continue to attack with high fastballs, though he probably should given the turn his career has taken. Another double digit strikeout game seems unlikely, but with how good Chen has been at home there is at least a modicum of streaming value with him.

If not even, most home/road ERA splits are within a run or two of each other, sometimes large enough to raise question, but rarely large enough to be answered by something other than small sample size. In Chen’s case there isn’t a one or two run difference in ERA, but a 7.51 run difference. You could take Chen’s 9.35 ERA on the road, subtract Jason Vargas’ 6.96 ERA, and then you’d have a reasonable gap between Chen’s home/road ERA. While utterly useless in the grand scheme of things, that exercise not only demonstrates how ridiculous Chen’s splits are, but affords us the opportunity to throw shade at Jason Vargas. These splits aren’t all luck related either. Chen does have a .238 BABIP at home and a .327 BABIP on the road, but his K/BB ratio, HR/9, and FIP are all over 1.8 times worse on the road.

Chen has three colossal blowups on the road this season. A three inning, nine run shelling by the Cubs, a four inning, seven run outing at Coors Field, and a 4.1 inning, seven run pounding by the Nationals. If we subtract those three outings his road ERA lowers to 6.19. Still terrible, and to speak candidly when I began that exercise I expected his ERA to be better by subtracting those horrific outings. And by the way, those outings shouldn’t be ignored. We can excuse one outing like that a season; blow ups happen to most sub-elite pitchers. We can’t excuse all of them, and if we did Dylan Bundy would be a superstar.

Ultimately, what we have with Chen’s home/road splits is a question that can’t be definitively and tangibly answered. Before this season Chen had better road splits, with a 4.06 ERA at home and a 3.73 ERA on the road for his career. He did spend the first four seasons of his career in Baltimore, but he also spent two in Miami before this year. Also, before this season Chen had a 5.70 ERA at home and a 3.90 ERA on the road in a Marlins uniform. Really Chen is just a below average pitcher and his skill is manifesting itself in odd ways that make it seem like a pattern, but truly he just isn't that special.

Verdict:

Chen threw the high heat in this one to rack up impressive and uncharacteristic strikeout totals. These strikeout numbers may be short-lived if the league catches up or if he simply reverts back to old ways. His massive home/road splits have be a mystery to many baseball fans, analysts, and even the Marlins. There is no definitive answer for his splits, but the sum of the parts looks like a high-fours ERA pitcher with low dominance and a home run problem. Because he’s been so good at home Chen is a desperation streamer in Marlins Park, but not trustworthy on the road or against an above average lineup.

Michael Kopech, Chicago White Sox

2018 Stats (Triple-A): 126.1 IP, 3.70 ERA, 3.30 FIP, 2.83 K/BB ratio

08/21 vs. MIN: 2 IP, 3 H, 0 ER, 0 BB, 4 K

08/26 @ DET: 6 IP, 7 H, 1 ER, 0 BB, 4 K

The chosen one has arrived, and while the legend of Michael Kopech has grown to Paul Bunyan levels of exaggeration over the past few years he did not disappoint during his first week in the majors. His first outing against the Twins was cut short by rain, but he got a full start against the Tigers on Sunday. His fastball was on full display in these two games, as the threw it 69.5% of the time in eight innings. He used his slider 24% of the time, and went to the changeup just 6.5% of the time. The average fastball velocity was lowered than expected at 96 MPH, but he touched 99 and was consistently able to pop 97-98 early in the game. Kopech had 15 total swinging strikes between these starts, eight of which came from his fastball. He didn’t maintain the lofty 12 K/9 rate he had in the minors, but Kopech put up decent strikeout numbers in the two appearances.

In the game against the Twins Kopech was horribly inefficient with his pitches, and he labored through 52 pitches to get six outs. He was drenched in sweat and looked gassed before the game even started. That may have been debut jitters, or Kopech may be a heavy sweater, but it seemed like every pitch was overly taxing and max effort. He was able to get four strikeouts to zero walks, but batters worked long at-bats against him all game. Only so much can be gleaned from a two-inning outing, but the raw stuff looked legitimate against the Twins.

The game against the Tigers started out great, but Kopech’s velocity waned as the game went on and he ran into trouble in the sixth. He surrendered back-to-back doubles and it took a great catch from Adam Engel and a double play to limit the damage to one run. He was throwing between 93-95 MPH by the sixth inning, which is concerning considering he only threw 86 pitches total. He got his last strikeout in the fourth inning, and that is also when his velocity decline began. He’s been starting all season in the minors, so Kopech is used to a starter’s workload. His fastball isn’t just velocity; it has above average horizontal movement and an elite spin rate at 2565 RPM on average. Still, if he is throwing four or five MPH slower by the sixth inning there is a problem here.

This was his first full major league start, so we’ll have to see whether this is a common trend for him as he pitches deeper into games. Kopech has a smooth delivery until the end, where he does a violent, whipping motion with his arm. Kopech is often compared to Noah Syndergaard, and it’s easy to see why in his delivery. There should be depth concerns with Kopech on a start-by-start basis. He has shown to be inefficient with his pitches and had a hard time lasting deep into his start against the Tigers. He also had control issues in the minors, walking 11% of the batters he faced at Triple-A this season. He hasn’t walked a batter in either of these starts, but he runs the count high often and hit two Tigers on Sunday. The pitches that hit the batters missed horribly too, and he nearly took Mikie Mahtook’s head off at one point. Kopech is an unseasoned, unfinished product. That doesn’t mean he shouldn’t be added, or that he won’t be valuable down the stretch, but it means he might not be the ace we hoped for right away.

Verdict:

Kopech had moments of brilliance between the two starts, and some of the pitches he threw make it easy to buy the hype. His velocity waned as the start in Detroit went on, and his control issues were present even though he hasn’t walked anyone. He’s not the superstar pitcher we hoped for yet, but he is a must add just on talent alone. Kopech should be a good source of strikeouts and hopefully ratios during the final month, though wins and even quality starts may be hard to come by for a young pitcher on the White Sox.

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