Statcast Pitcher Studs and Duds - SIERA Analysis for Week 6

Welcome back to RotoBaller’s Statcast pitcher Studs and Duds article series! Each week I will select an advanced stat, choose two top performers and two under-performers, and analyze what those stats could mean for future fantasy output. Now roughly a month into the season, we are starting to gather a decent sample of data for pitchers, which can help paint a clearer picture as to whether or not players will continue to perform as they have. It seems like a good time to focus on one of my favorite advanced metrics; skill-interactive earned run average (SIERA).

SIERA is a great metric for capturing a pitcher's independent performance. It quantifies a pitcher's performance by trying to eliminate factors the pitcher can't control on their own. Fielding-independent pitching (FIP) is a stat that also attempts to do this, but unlike FIP, SIERA considers balls in play and adjusts for the type of ball in play. The formula can be found here for those who want to get into the nitty gritty.

SIERA is a truer indicator of a pitcher's performance than ERA or FIP and can help predict future success or failure compared to a pitcher’s current ERA (which I will do an article on a bit later in the season). It is a great metric for identifying potential buy-low and sell-high candidates, so this will hopefully be a helpful article for those of you taking a look!

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Top SIERA Pitchers

All stats current as of Sunday, May 2.

Joe Musgrove, San Diego Padres

(2-3, 2.38 ERA, 0.74 WHIP, 2.22 SIERA)

This first pitcher has been one of baseball's best to start the season. Joe Musgrove has been a huge asset in his first season with the Padres, compiling a stellar 2.38 ERA and 37.3% strikeout rate. Oh, and he also threw the first no-hitter in Padres history! Perhaps more importantly, he also has one of baseball's lowest SIERA's at 2.22. Can Musgrove continue to be one of baseball's top pitchers?

Let's first take a look at Musgrove's batted-ball profile, as that is an important part of SIERA. His avoidance of hard contact and his launch angle definitely check out. His average exit velocity and hard-hit rate are in the 72nd percentile and 66th percentile of baseball, respectively, and his 8.9-degree average launch angle is below league average.

Musgrove's strikeout rate also doesn't seem all that outlandish. He has done a nice job mixing his pitches. He has five pitches that he throws with at least 10% frequency. In fact, his most-frequently thrown pitch is his slider at 27%. The important thing is that Musgrove has achieved at least a 13% swinging-strike rate with each of his three most-used pitches, with the best coming from his slider at a crazy 29.2%. While this mark may not stand, I see no reason for Musgrove's strikeout rate to suddenly plummet if he continues to mix his pitches.

Things have started off great for Musgrove, and there are no underlying signs to suggest that things will get worse any time soon. He has avoided hard contact and has been striking hitters out. All of this has been supported by his SIERA, and I'm buying it until the numbers suggest otherwise.

Carlos Rodon, Chicago White Sox

(4-0, 0.72 ERA, 0.64 WHIP, 2.76 SIERA)

Carlos Rodon is a pitcher who fantasy managers have hoped would blossom into a higher-end fantasy starter for years now. However, poor performance and injuries have held him back for much of his career. Things may finally be coming to fruition for him in 2021. Rodon has started the season with a 4-0 record, a 0.72 ERA, a 37.9% strikeout rate, and a 2.76 SIERA that is eighth-best among qualified pitchers. And let's not forget a no-hitter of his own! Can fantasy managers buy into his hot start? 

Let's first take a look at his batted-ball profile. Rodon's 88.9-MPH average exit velocity is in the middle of the pack across baseball and is in line with his 88.8-MPH career mark while his 41.3% hard-hit rate is slightly below league average. Further, he has allowed an average 15.7-degree launch angle to this point. The good thing is that Rodon has allowed the fourth-lowest contact rate among qualifying pitchers this season. The bad thing is that this batted-ball profile does not bode well overall despite his SIERA, especially given that it matches his career profile, which has not typically led to success.

In terms of his ridiculous strikeout rate, Rodon can thank his slider in part. He has generated an impressive 21% swinging-strike rate with the pitch, which has slightly above-average vertical movement but has much more horizontal movement than most sliders in the league. He also can thank his fastball, which has above-average velocity at 94.9 MPH, league-average spin, but a 17.3% swinging-strike rate. The slider swinging-strike rate seems believable, but such a high rate for a starter's fastball does not seem sustainable. Rodon does have the advantage of locating that pitch in the top of the zone with his velocity, but I do not believe that such a high mark is achievable over the course of an entire season.

In sum, Rodon has pitched quite well so far and has one of the league's best SIERA's to show for it. However, his 2.76 SIERA is almost two runs higher than his ERA, which is a big discrepancy. Further, his batted-ball profile suggests to me that a projected 2.76 ERA is being generous. Finally, his insane strikeout rate is being bolstered by a crazy swinging-strike rate on his fastball. I wouldn't definitively say that Rodon is a sell-high candidate since he has quite a lot of room for negative regression while still being a fantasy contributor. That being said, I would part with him for a generous trade offer.

Bottom SIERA Pitchers

All stats current as of Sunday, May 2.

Taijuan Walker, New York Mets

(1-1, 3.00 ERA, 1.26 WHIP, 4.72 SIERA)

While it is rare, some pitchers can consistently outperform their batted-ball profiles or SIERA's. It seems like Taijuan Walker may be one of those pitchers. Walker has a career 3.80 ERA and is off to an even better start this season, compiling a 3.00 ERA with a 23.9% strikeout rate over his first five starts. The confusing thing is that he has a career 4.15 SIERA and currently has a 4.72 SIERA. What should fantasy managers make of this as the season continues?

The picture is pretty straightforward on Walker to this point. He has allowed hard contact with a 13.1-degree launch angle, and has below-average expected stats to show for it. The one thing to note here is that Walker's expected stats are higher than his career numbers across the board, yet his batted-ball profile is similar. This indicates that his expected stats may be a bit unfair to him right now, but the fact remains that signs point to Walker outperforming himself.

Walker has been a useful fantasy pitcher so far, but his SIERA and accompanying expected statistics suggest that he has gotten lucky to this point. The difficult thing here is that Walker doesn't stand out as a fantasy stud, which would make it difficult to sell high on him. Given that he has outperformed his SIERA throughout his career, my verdict would be for fantasy managers to stick with him as long as he continues to get positive results.

Matthew Boyd, Detroit Tigers

(2-3, 2.27 ERA, 0.93 WHIP, 4.66 SIERA)

Our final pitcher is one who has showed signs of potential over the course of his career but has never managed to put all the pieces together. It finally looks like he may be now to start 2021. Matthew Boyd has gotten off to a nice start to the season, posting a stellar 2.27 ERA and 0.93 WHIP. However, his 4.66 SIERA is ninth-highest among qualified pitchers. Should fantasy managers look to trade Boyd now while they still can?

A deeper look into his batted-ball profile gives mixed messages. Boyd has done a decent job of avoiding hard contact. His 86.7-MPH average exit velocity is in the 78th percentile of baseball and his 36.2% hard-hit rate is in the 63rd percentile of baseball. On the other hand, his 19.7-degree launch angle leaves something to be desired. As I discussed in my last two articles, hard contact or a high launch angle does not necessarily mean that a pitcher won't be successful. Boyd's batted-ball profile isn't awful, but his SIERA suggests that it may catch up to him.

Looking further into his pitch mix, Boyd has relied mostly on a fastball, changeup, and slider. His fastball and slider location have been good, but he will struggle to find success if he keeps leaving his changeup in the middle of the plate. While his location has been fine overall, his strikeout rate has not been, as his 17.3% mark is a good deal lower than his 22.5% career value. The culprit has been his slider. His fastball and changeup swinging-strike rates have been pretty consistent with his career marks, but he has generated just a 9% swinging-strike rate this season with his slider compared to a 16.8% career average. This is curious, as Boyd's slider has nearly identical velocity and spin rate to the pitch over the past several seasons. As such, I would expect to see Boyd start to get some more strikeouts with the slider due to regression to the average.

It is difficult to draw a firm conclusion on Boyd at this point. He has gotten great surface results and does have some underlying stats to support them, but also has some potentially detrimental signs as well. Boyd has been hyped up by fantasy managers before but has never fully delivered. While this looks like another chance to do so, I simply can't believe that his performance is legitimate until I see more examples of Boyd reproducing the numbers he has to this point.

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