Any time is a good time to check in on reliever leaderboards to try and spot a couple loose canons for hire off the ol’ Waiver Wire, but I’ve always tended to gravitate towards this particular time of year for a more in-depth stock check. We’ve got a nice combination of half-season performance from some of the older-hat options along with some dynamic recent recalls sprinkled in, so it’s a particularly fertile opportunity to add ratio support to your bullpen before the final push to most trading deadlines begins. The PITCHf/x leaderboards have glorious hallways in which to wander searching for sound investments, and to that end here’s a sample of four relievers who’ve caught my eye as potential second-half assets in formats that value bullpen arms for one reason or another.

Justin Wilson, LHP, Detroit Tigers

He made some noise last year in producing the fourth-most holds in baseball, and doing so with solid-if-unspectacular ratios to boot. But he’s taken things to a next level this year, currently boasting the sixth-best cFIP of any reliever. And yet somehow his ownership rates – currently just four percent in Sportsline leagues – don’t really seem to reflect his dominance. I suspect this is due to a couple clustered multi-run outings earlier in the year, but that’s really no excuse. He’s gone from being a predominantly four-seam guy who mixed in a cutter and sinker to an increasingly even three-pitch mix guy, with the gains in cutter deployment especially noteworthy as a driving factor for his breakout. He’s getting more swings against his cutter than any other reliever who throws the pitch, and when batters swing at it they miss it entirely more than a third of the time (ninth-best rate) and pound it into the ground eight times for every one they manage to lift (second-best rate). Overall his groundball rate has skyrocketed by 13 percentage points year to year. Not having to overly rely on the four-seamer has also helped that already-potent pitch to play up as well, to where that pitch is now producing the sixth-best whiff-per-swing rate among relievers, a couple ticks better than Jeurys Familia‘s. He’s really good at getting out righties and lefties alike, and if you play in a holds league he’s probably already on someone else’s team. But there’s really no reason he should be available in any league in which middle men have even cursory rate-stat value.

Edwin Diaz, RHP, Seattle Mariners

I’m not going to spend too much time on Diaz, whose prospect stock was more well-known to where his initial success has already begun driving an ownership spike as he’s come into the league and piled up whiffs out of the gate. He’s had a really weird start to his career though, where his four-seam fastball has been getting popped to the tune of a 30 percent line-drive rate and .524 ensuing BABIP despite sitting 96-97 with well above-average run. In spite of the undue number of runners reaching against him, he’s managed to strand an absurdly high number of them, and the net has been a pretty dominant run-prevention effort with elite strikeout totals sprinkled in. His slider has been a legit out pitch, with a two-thirds rate of swings and a borderline top-ten swing-and-miss rate against it. He has taken to his bullpen role really, really well, in other words, and given the pedigree he should be among the most targeted middle men currently available on about 90 percent of waiver wires.

Dario Alvarez, LHP, Atlanta Braves

It’s okay, I hadn’t heard of him until just a few days ago either. Alvarez is 27, and while he always posted groovy whiff rates throughout his minor-league career. it was more of a “this guy’s tough to pick up from the left side, and his slider’s good enough to play off a low-90s fastball” kind of a profile. A best-case situational relief profile, that. Well, the Mets put him on waivers earlier this spring, the Braves claimed him, and when he got recalled in mid-June suddenly he was sitting at 94 (up four full miles-per-hour from last September) with the slider coming in three clicks faster. And lo, he has now struck out 19 of the first 35 batters he’s faced for Atlanta, with a lone solo shot marring his season’s line.

We’re obviously working with extremely limited samples so far, but his 58.7 percent whiff-per-swing rate on the slider is fourth-best among all relievers to throw at least 75 of ’em this year, and he’s inducing offers at a well above-average clip. The four-seamer’s doing solid work missing bats in its own right, and he’s shed his LOOGY-in-waiting tag to be a more or less equal-opportunity destroyer thus far. His pitch movement isn’t particularly out of line with previous efforts despite the extra punch, but Atlanta appears to have unlocked his potential by pretty dramatically altering his plan of attack. He’s been much more effective at working the fastball up in the zone and starting the slider on a similar trajectory before taking it down to finish marginally below the zone. He should already be on the radars of deep leaguers, and if the performance continues to hold against right-handers to where he can escape a situational role, he’ll have appeal to shallower and shallower leagues based on the elite strikeout potential.

Tony Barnette, RHP, Texas Rangers

Hey, it’s a 32-year-old rookie with a strikeout rate south of 18 percent! Barnette is one of the cooler under-the-radar stories of the season, as a former 11th-rounder who migrated to Japan after stalling out in Triple-A in 2009, evolved into a top-tier closer for the Yakult Swallows, then signed a two-year deal to return to the States this spring. He came out of the gate working off a four-seam-slider combination, but that has rapidly evolved into a cutter- and, increasingly, curveball-dominant repertoire. And that transformation has been well-founded, as his hook has shown to be among the most dominant deuces in any bullpen league-wide. He’s generated the seventh-highest swing rate against his curve, and for every two a hitter has swung at he’s come up empty on one of them. The pitch boasts some of the hardest horizontal movement you’ll see, and he’s significantly ramped up his usage over his last six appearances, during which he’s gone nine scoreless innings with eight strikeouts and only three hits allowed. There’s a not-insignificant platoon issue involved here, but AL-only players should nod the head up and toss him onto a watch list to monitor how the cutter-curve combo plays over his next couple outings.

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Thanks, interesting reading!