Statcast Pitcher Risers/Fallers - Monthly xwOBA Splits (Week 10)

Welcome back to Rotoballer's series using Statcast to extrapolate, dig into, and commiserate over data to examine pitching performances. The weekly series will be dynamic as we fine-tune our findings and enlighten ourselves on the information and tools at our disposal.

All savvy fantasy players know that when we scour the trade block or waiver wire for pitchers, the season-long body of work becomes less important as the year progresses. When weighing transactions, owners don't want to make the mistake of overpaying for a guy that performed great in April but has since gone the way of Sidney Ponson. Sure, consistency is the name of the game, but market timing also is critical in assessing player value. We've turned the calendar to June and it's fair to start comparing periodic splits.

Way back in Week 5, we discussed the topic of wOBA and xwOBA to observe how the differences in the two metrics could help identify anomalies in pitching performance. As a reminder, wOBA measures the actual outcome of an at-bat while xwOBA determines the expected outcomes of that same at-bat based on Statcast information like exit velocity and launch angle. Since this is a Statcast series, let's focus on the latter. Today we'll compare the difference in xwOBA for starters between the months of April and May to categorize our risers and fallers.

Bound to Pop

All stats as of May 31 for pitchers that threw over 400 pitches in both April (125 total) and May (122).

Caleb Smith, Miami Marlins (4-5, 3.51 ERA, 1.15 WHIP, 11.02 K/9)

Few people outside of Miami knew of Caleb Smith entering 2018. Come to think of it, most Miamians probably didn't know about him either. Smith had a forgettable start to the season, ending April with a 4.40 ERA and 1.26 WHIP. His xwOBA was a pedestrian .318. In May, that xwOBA improved to .284 which was good for 17th-best in the majors. The results were excellent, Smith posted a 2.60 ERA and 1.05 WHIP for the month.

So what changed? His pitch velocity and movements look the same month-to-month and he still relies on three pitches. The difference might be deception and pitching to soft contact. In April, Smith registered a 12.7 K/9 by emphasizing his fastball-slider. Strikeouts are fine, but they were paired with ugly, unusable ratios. In May, he peeled back the power pitches and threw his changeup more often. The K/9 declined to 9.1, but his opponent slugging percentage dropped significantly. By upping the changeup usage to only 15%, Smith increased the pitch values for his entire arsenal.

With current trends, the K/9 outlook for Smith may drop to about one per inning. Fantasy owners will gladly take that for the existing 3.21 FIP the rest of the way. The .260 BABIP is probably too low and he has control problems (4.2 BB/9), but if Smith continues keeping hitters off balanced, the fly ball-heavy pitcher (48.9% FB%) should keep reaping the rewards of spacious Marlins Park.

Tanner Roark, Washington Nationals (2-5, 3.38 ERA, 1.07 WHIP, 7.63 K/9)

Not sure I've ever pounded the table on Tanner Roark. So this is weird. But recency bias aside, Roark has been solid through his career (3.41 ERA, 1.18 WHIP). The guy deserves his fair shake. Roark improved from an unflattering .343 xwOBA in April to the 20th-lowest .288 in May. The headline returns for Roark were actually better in April, so the conclusion is he could presently be experiencing better aggregate numbers.

Roark is a five-pitch guru and has always enjoyed positive pitch values across the board. He started the year throwing more power pitches, and has since tapered that to focus on more changeups and curveballs. The results are higher whiff percentages for his primary fastball (8.3% to 11.7%) and sinker (3.1% to 7.1%). Both pitches also saw drops in opponent slugging, most notably in the fastball from .400 to .048. Make no mistake, Roark still greatly depends on his fastball-sinker (54.3% combined), but he's done an excellent job sprinkling in secondary pitches.

Roark's .241 BABIP certainly suggests batted-balls will drop more frequently. But if he holds them to singles (21.2% Soft%), he may yet avoid the dreaded blowup innings. His lack of strikeouts makes him a very unsexy fantasy starter and results in an unremarkable K/BB (2.5), but Roark's proven himself a reliable asset. Taking advantage on his meh profile could be a great opportunity for owners to pocket a steady weekly starter.

Other possible risers: James Paxton (SEA, .321 April xwOBA vs. .275 May xwOBA), Vince Velasquez (PHI, .304/.251), Luis Castillo (CIN, .392/.298)

Due to Drop

Rick Porcello, Boston Red Sox (7-2, 3.65 ERA, 1.14 WHIP, 8.51 K/9)

We touched on Rick Porcello in Week 4, who at the time held a sparkling 1.40 ERA and 0.82 WHIP. My bear argument against him was that his exit velocity was materially lower than the EV during his 2016 Cy Young campaign. Porcello believers could've countered with his .246 April xwOBA. That measure spiked up to .340 in May to accompany an awful 5.35 ERA and 1.49 month.

Unfortunately, we're not here to bask in glory. But the previous fortunes of his LD%, HR/FB and LOB% have evaporated. For his part, and reasons unbeknownst to me, Porcello has dialed back his sinker usage and is leaning more on a curveball, effectively trading a pitch he's been historically good at for one he's struggled with. Hmm. Not surprisingly, the change in pitch approach has led to higher opponent slugging for every one of his pitches. In May, Porcello's four-seamer is surrendering a 46.2% LD% and .348 ISO. If his adjustments after April were intentional, it might be back to the drawing board.

Porcello's name brand and early-season triumphs may buoy his marketplace value. The seven wins on a powerhouse Red Sox team also helps. But Porcello has settled into an eerily similar resume as 2017's disappointing season. Porcello is worth shopping to owners in need of wins, or any BoSox loyalists turning a blind eye to his melting peripherals.

Alex Wood, Los Angeles Dodgers (1-4, 3.75 ERA, 1.04 WHIP, 8.37 K/9)

Alex Wood has suffered a more precipitous drop in xwOBA than Porcello. His excellent .248 April xwOBA turned into the league's 85th-worst .349 in May. Unlike Porcello, Wood's May returns were decent (3.29 ERA, 1.24 WHIP), masking the Statcast voice of reason. Wood's 2018 3.20 FIP is actually superior to last year's breakout season (3.32).

Wood is an odd pitcher that has no traditional four-seam fastball, exclusively using a sinker, slider and changeup. As the season's gone on, Wood's increased his sinker usage from 39% to 49%. Velocity-wise, it's remained constant but he's lost some horizontal break. The ISO on the pitch has increased from .194 to .209, modest but possibly meaningful. What is noteworthy to point out is the changeup that he's cut back from 34% to 27% has experienced massive deterioration, experiencing a BAA of .406 and opponent slugging of .625. Either he's lost confidence in the pitch, or a mechanical change has resulted in that pitch becoming a meatball.

We're not arguing that Wood is in for an imminent collapse. But for a guy without a fastball, a worthless changeup can reduce him into a two-pitch pony real quickly. He has the pedigree and recent success to figure things out, but it personally seems difficult to trust. We'll see as the season unfolds, but recognizing the mismatch between his May numbers and xwOBA, Wood is not a desirable roster piece.

Other possible fallers: Gerrit Cole (HOU, .247 April xwOBA vs. .291 May xwOBA), Sean Manaea (OAK, .287/.431), Lance McCullers Jr. (HOU, .280/.345)

More Sabermetrics & Fantasy Baseball Strategy