By Joe Sparacio

We know how invaluable great closers can be -- last year alone we saw the Cubs trade their top prospect for Aroldis Chapman, who helped them win the World Series, and the Giants sign Mark Melancon for $60 million because their bullpen was a mess. But entering the season, everyone knows that a closer's job is also only as secure as his unhittable stuff. Once a reliever gets into a rut, they can quickly move down the depth chart.

Take Tony Watson into account. The longtime setup man for the Pirates was given the closer's role at the end of last year. He was doing fine to start the season in Pittsburgh, converting his first seven save chances and giving up only one homer in April. Then it came crashing down in May. Watson blew three of six save chances and then blew two more this past week, watching as his ERA ballooned from 0.96 to 4.44. As of Friday, the Pirates decided to make a switch, removing Watson from the closer's role and instead splitting the duties between a reinvigorated Juan Nicasio and a talented southpaw Felipe Rivero while Watson tries to regain his stuff. 

Let's take a quick look at some of the more tenuous closer situations around the Majors with a little help from MLB Fantasy411's Closer Report.

Nationals

Closer: Koda Glover
Possible save candidates: Matt Albers, Shawn Kelley

All eyes will likely be on this bullpen for the entire baseball season … that is until the Nats possibly trade for a bona fide stud closer at the July 31 non-waiver Trade Deadline. Glover has the job right now after losing it earlier in the season, and there's talk that Washington wants the young fireballer to be its closer of the future, but it looks like he might need some more seasoning.

Waiting in the wings are a pair of veterans: Kelley was lights-out last season but has struggled out of the gate this year. Albers, meanwhile, has a career ERA over 4.00 and doesn't look like the future at the back end of the 'pen.

Mariners

Closer: Edwin Diaz
Possible save candidates: Nick Vincent, Tony Zych

Seattle has the best shaky bullpen in the Majors, if that makes sense. Diaz had a brief hiccup where he lost the job in April, but now seems to have it back. It helps that he throws 100 mph along with an absurd wipeout pitch. Unfortunately, with that hard-throwing capability comes struggles with location and control, and thus we've seen him given a break from the ninth inning.

Waiting in the wings are Vincent, who boasts an ERA near 2.00, and Zych, possibly one of the most underrated relievers in the Majors. Last season, Zych struck out over 13 batters per nine innings. If he could get that number back up, he has a chance to give Diaz a run for his money in that closer role. 

Phillies

Closer: Pat Neshek
Possible save candidates: Hector Neris, Joaquin Benoit

The back end of this bullpen is filled with a group of veterans and a youngster Neris, who is likely still the closer of the future, but right now can't seem to locate his devastating splitter. Though he was dominant last season with a 11.4 K/9, hitters are beginning to square up more on Neris' other pitches and his effectiveness has gone down.

The veterans have been given the closer role in the meantime. Neshek has been handed the job after his strong setup work , but he is likely to get flipped at the Trade Deadline. Benoit was strong to start the season and has had numerous closer gigs in the past, but his problem has always been health and he is on the DL again. Jeanmar Gomez is technically still around, too.

Padres

Closer: Brandon Maurer
Possible saves candidates: Brad Hand, Carter Capps

The Padres are likely feeling out their bullpen candidates this season as the team looks toward the future. This means that the closer job is relatively up for grabs and one of these three guys will likely have it locked by season's end. Hand seems like the best reliever in the bullpen right now, and the way the team looks, he actually has a chance to represent San Diego in the All-Star Game. But he is also a trade candidate. Maurer was the incumbent closer after taking over the role at the end of 2016, but his rate stats have been less than impressive. He currently sports a 6.75 ERA.

Capps is the wild card in this 'pen. He is preparing to face live hitters after a stint on the DL, but who knows what his stuff will look like now. His strikeout rates have always been off the charts, but his mechanics are so wild that they caused MLB to make some pitching rule clarifications.

Athletics

Closer: Santiago Casilla
Possible saves candidates: Ryan Madson, Sean Doolittle

Over in Oakland, save candidates abound. It looks like Casilla finally has the job after moving across the Bay from San Francisco, but the veteran isn't a hard thrower and. as his peripherals show, he might be losing his touch.

Madson has been in and out of the closer role, as has Doolitle, but both have struggled in the past shutting the door. This season, Madson has been reliable with eight holds and will likely get a chance to take over the job (or get traded to a contender for his efforts). Doolittle, meanwhile, will likely get a crack late in the season after he proves that he can stay healthy.

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Joe Sparacio is an associate producer for Sports on Earth. Follow him on Twitter @joetsparacio.