The waiver wire. Free agent budgets (FAB). It's back, it's real and it's glorious.

With the 2021 baseball season in full swing, nailing the waiver wire and the players available are critical to beating out your league-mates in season-long leagues.

Each week we will take a look at players who are rostered in fewer than 50% of Yahoo leagues and can help out your season-long squads. Remember, if you aren’t scouring the waiver wire, you are falling behind.

Kyle Muller, SP, Atlanta Braves

Roster Percentage: 6%

While the Atlanta Braves have desperately tried to identify some young arms like Ian Anderson to supplement their rotation, which is even more imperative with teammate Mike Soroka re-injuring his Achilles, Kyle Muller has shown some major promise to start his young career.

After dueling with Jacob deGrom in his first start, dropping a narrow decision, Muller marched into Cincinnati and fired five scoreless frames, whiffing nine Cincinnati hitters.

He's widely available in most leagues and likely has a rotation gig moving forward, so keep an eye on him.

Amir Garrett, RP, Cincinnati Reds

Roster Percentage: 31%

Bullpens are a unique circumstance to manage, and 2021 has made that no exception. Thanks to a slew of injuries to bullpen mates Lucas Sims and Tejay Antone, Amir Garrett was given an opportunity to take the job for the Cincinnati Reds, and for now, it looks like he has it.

Now you could be scared off by the season-long numbers, and for good measure -- Garrett sports an ugly 7.71 ERA and 1.59 WHIP this season. But he's converted three saves in the last two weeks, and he does provide plenty of strikeouts, notching 29 in 23 1/3 innings pitched this season, to be precise.

Consider Garrett to shore up your bullpen.

Hunter Renfroe, OF, Boston Red Sox

Roster Percentage: 25%

Veteran Hunter Renfroe of the Boston Red Sox is in the midst of one of his patented hot streaks, and now is the time to give him an add.

Up to nine long balls this season, Renfroe has been an on-base machine as of late. Over the last two weeks, he's managed to get on base at a .412 clip, knocking in 10 runs.

On one of the few teams with seven games next week, Renfroe deserves a long look.

Tarik Skubal, SP, Detroit Tigers

Roster Percentage: 49%

If you can tame the best offense in Major League Baseball -- the Houston Astros -- you deserve a look. If you've been dominating for the last month or so, as Tarik Skubal has, you are worthy of a lot more attention.

Spanning the last month, the young southpaw has logged 33 1/3 innings, and he has been spectacular, amassing 43 strikeouts, a 2.70 ERA, and a 1.20 WHIP.

On Sunday, Skubal terrorized the Houston Astros, and he's been nearly unhittable since a rough start to the season. Consider Skubal if you need rotation help.

Notable Two-Start Pitchers to Consider This Week

Eli Morgan (CLE) -- vs DET, vs HOU
Chris Flexen (SEA) -- at TOR, vs TEX
Joe Ross (WAS) -- vs NYM, vs LAD

Games in Coors Field This Week

Pittsburgh Pirates (3), St. Louis Cardinals (4; Lars Nootbaar season!)