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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.
We've rolled over the All-Star break and the trade deadline is fast approaching. With myriad players likely on the move over the next week, we'll shift gears in Week 17 and look at baseball's most coveted and reliable commodities, relief pitchers. Our Statcast series has focused solely on starting pitchers, but we'll hop on the trade bandwagon to review which relievers are ones to target or avoid.
The Statcast metric we'll use is a familiar one, xwOBA and its differential to wOBA. In our qualified pool of 64 relievers, the median xwOBA is .287. Real-life trade potential will be assigned marginal credit, as most relievers provide standalone fantasy value regardless of save opportunities. Our in-depth candidates are currently closers, but the collection of "other" players could also be keen pickups and drops to protect multiple pitching categories down the stretch.
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Relievers to Target
All stats as of July 24 for 64 relief pitchers with a minimum of 150 plate appearances against.
Wade Davis, Colorado Rockies (4.61 ERA, 1.22 WHIP, 9.88 K/9, 28 Saves)
Wade Davis is fresh off a five-run implosion against the Astros on July 24 so the timing on this bullish call is impeccable. Davis has a passable .273 xwOBA but the .024 differential against his wOBA (.297) is ninth-widest amongst relievers. With the Rockies in the thick of another NL West race, Davis is likely a fixture in Colorado for the rest of 2018.
Davis has endured a relatively rough season, highlighted by career-high hard contact (33.3%) and walk rates (4.61 BB/9), but he's trending positively. Prior to the aforementioned meltdown, Davis had allowed only two earned runs in his last 12 outings (1.50 ERA), posting a 0.75 WHIP and 9.75 K/9 along the way. While his dominant cutter has retreated this year, opponents are slugging a measly .143 against the pitch in July. Davis struggled in May and June, but pitch effectiveness for his fastball-cutter combination is starting to normalize in-line with career averages.
Before the transitory swoon, Davis enjoyed a fantastic April in his Rockies debut (2.61 ERA, 0.87 WHIP). Walks appear the determinant factor to his second-half success. Improve location and he should succeed in setting up the killer cutter. Davis could likely be nabbed at a discount in fantasy leagues, a reversion to the lockdown reliever of the past four years seems just around the corner.
Brad Boxberger, Arizona Diamondbacks (2.89 ERA, 1.15 WHIP, 12.54 K/9, 24 Saves)
Lifetime reliever Brad Boxberger has embraced his first year as a full-time closer, pacing better than career trends in ERA, strikeouts and walks. Boxberger sits in the top-15 in xwOBA (.268) yet also experiences an unfavorable delta of .009 compared to his wOBA (.277). Similar to Davis, Boxberger and the D-Backs are entrenched in a tight pennant race, securing his season-long closer value.
Dissimilar to Davis, Boxberger has been a model of consistency. Excluding a four-run debacle on June 17 against the Mets, he has given up only eight earned runs this season. The blip hasn't phased the veteran, Boxberger is registering a .040 BAA and 0.50 WHIP in eight July appearances. The key change in Boxberger's approach in 2018 has been the abandonment of a previously terrible slider. He's narrowed his arsenal to a pure fastball-changeup combination which has diminished the risk of unwanted meatballs. Boxberger has maintained a steady 12 MPH differential between the two pitches, generating strong whiff rates and positive pitch values for both.
Naysayers can point to Boxberger's FIP (3.99) and BABIP (.244) to question his worth. A 44.0% Hard% could be concerning, but the damage has been limited to worm burners (51.2% GB%). It's not farfetched to imagine he'll encounter a handful of slipups to reconcile the ERA and FIP disparity, but the dependable save chances and strikeouts should play in any league.
Other attractive relievers: Zach Duke (MIN, .049 wOBA/xwOBA differential), Ryan Tepera (TOR, .034), Shane Greene (DET, .020)
Relievers to Avoid
Raisel Iglesias, Cincinnati Reds (2.20 ERA, 0.98 WHIP, 9.40 K/9, 19 Saves)
Despite a very strong season to-date, Raisel Iglesias rings the alarm bells with a .321 xwOBA that's .065 points higher than his wOBA (.256). That gap is the third-most fortuitous in our reliever pool. Ignoring outstanding trade rumors, we'll observe Iglesias' pitcher-specific attributes for clues on his future performance.
Iglesias' success this season could be credited to the establishment of a phenomenal changeup to pair with his fastball-slider. He's upped the changeup mix to 22% this season, inducing a 26% whiff rate on the pitch and lifting his overall SwStr% to a career-best 15%. However, Iglesias has been losing velocity on all his pitches since May. While the change and slider have yet to show ill effect, Iglesias has been grooving more fastballs causing a jump in opponent slugging from .435 to .714 since May. Without a potent fastball, overall pitch effectiveness is at risk of broad deterioration.
While Iglesias rarely surrenders hard contact (34.8%), his 7.1% barrel rate is above average resulting in structurally elevated LD% (24.1%) and HR/FB (15.0%) tendencies. Iglesias also benefits from extremely lucky factors like LOB% (92.9%) and BABIP (.217). He's generating swings-and-misses, but the career-low K/9 doesn't support his ninth-best strand rate for relievers. Fantasy managers with pitching flexibility should consider him a frontline trade candidate to obtain other needs.
Blake Treinen, Oakland Athletics (1.06 ERA, 0.98 WHIP, 11.47 K/9, 25 Saves)
We touted Blake Treinen in the offseason as a sleeper and he's exceeded all reasonable expectations. Before we delve into Treinen's possible downfall, let's establish that the call is relative. Although he holds the sixth-best xwOBA of .252, his .205 wOBA is .047 points lower and ranks sixth-most favorable amongst relievers.
Treinen has ridden obnoxious 98 MPH fastballs and sinkers to excellent pitch values across his repertoire this season. However, line drives against the sinker has ticked up to 27% in July, leading him to deemphasize the pitch and lean more on his cutter. Said cutter is Treinen's worst pitch but he's increased its usage from 5% to over 10%. While Treinen's overall resume remains outstanding, the change in approach is at least puzzling and at worst a possible mechanical glitch for the All-Star.
Treinen's success is rooted in his ability to avoid sweet spots (1.4% Barrels/PA). But considering his low fly ball ratio (26.2%), the 3.1% HR/FB appears artificially low. Make no mistake, Treinen is having a breakout season and the A's competitiveness only solidifies his fantasy standing. But, those same elements that make him so attractive also inflate his trade value. No matter the talent, it's unusual for a pitcher's xwOBA and wOBA to remain disconnected. There could be no better time to reap top dollar from a team desperate for Treinen's services.
Other risky bullpen arms: David Robertson (NYY, -.041 wOBA/xwOBA differential), Kelvin Herrera (WAS, -.032), Joakim Soria (CHW, -.023)
