Relievers are the bread, eggs and milk of trade season, and with the August waiver deadline eliminated, contenders could stock up their bullpens earlier than ever. But what options are out there?

The short samples sizes found in 20 to 30 relief appearances can yield some misleading ERAs. So let’s dig a little deeper, with help from Statcast’s advanced metrics, to assign superlatives to five of the biggest names on the reliever market.

The all-around stud: Kirby Yates, Padres

MLB.com’s AJ Cassavell reported Friday that it would take an “overwhelming offer” to pry Yates, who is under contract control through 2020, away from San Diego. But Yates might be MLB’s top closer right now, and Padres general manager A.J. Preller will still get a barrage of phone calls -- particularly if his club slips further down the National League Wild Card standings. Beneath Yates’ 1.16 ERA and perfect 25-for-25 line in save opportunities is the game’s 10th-best whiff rate (misses/total swings) and fourth-best putaway rate (percentage of two-strike pitches converted for strikeouts).

But the best indicator of Yates’ dominance? That might be his .209 expected weighted on-base average (xwOBA), Statcast’s all-encompassing metric that estimates how pitchers should fare based on quality of contact and strikeouts. There are 331 pitchers who have faced at least 100 batters, and Yates is No. 1.

The flamethrower: Felipe Vázquez, Pirates

The Pirates, like the Padres with Yates, will look for a massive offer for Vazquez since he’s under team control for four more seasons. But his pure stuff is just as desirable as his contract. Only four pitchers in baseball are averaging a higher fastball velocity than Vazquez, whose 98.1 mph heater is also showing more spin than ever before.

Vazquez is allowing slightly more fly balls and hard contact this year, but with a 2.12 ERA and 36.7% strikeout rate, he’s not “struggling” by any means. There’s so much raw talent here, and it would be fun to see if Vazquez could be even better with a change of scenery.

The soft-contact specialist: Brad Hand, Indians

Hand is earning roughly $7.1 million this year and will make nearly $7.6 million next season (with a 2021 club option), so he and his team-friendly contract will be mentioned early and often for a second straight summer. And if the Indians can’t make up ground on the Twins in the AL Central, they could deal Hand while he’s still near the peak of his powers. At age 29, Hand likely won’t be more valuable as a trade asset than he will be in the coming weeks.

A’s star Matt Chapman is the only hitter to take Hand deep this year, and he’s also the only player who’s even barreled one of Hand’s 443 pitches. It’s a little concerning that Hand’s ground-ball rate has sliced in half from 2018, but he does boast one of the Majors’ top 10 popup rates -- and popups are the next-best thing to strikeouts.

The all-situations lefty: Will Smith, Giants

Smith features a three-quarter arm slot and a wicked slider from the left side, but righties (.503 OPS) are having just as tough a time against him as lefties (.530 OPS). Smith has held righties to a .286 slugging percentage, and Statcast data says that figure should be even lower. His .262 expected slugging (xSLG, which, like xwOBA, is based on quality of contact and strikeouts) allowed in the platoon “disadvantage” is second-best of any southpaw in baseball.

Smith will be a free agent four months from now, and Giants president of baseball operations Farhan Zaidi is looking to improve his inherited roster in every way possible. So, Smith is as likely as any reliever on this list to switch uniforms in the coming weeks.

The hidden gem: Jake Diekman, Royals

Diekman’s 4.66 ERA won’t jump out at you, but clubs already know that he’d come cheap with a $2.25 million salary (and a reasonable $5.75 million club option for 2020). They probably also know his ERA is due for a reduction.

Diekman’s .285 expected slugging and .187 expected batting average allowed rank in baseball’s 96th and 95th percentiles, respectively. Behind those figures are Diekman’s excellent 34.6% strikeout rate and his solid ground-ball (45.2%) and popup (14.5%) rates. As an inexpensive southpaw who misses bats and racks up weak contact, Diekman should drum up plenty of phone calls to Royals general manager Dayton Moore.