NFL Free Agents 2015: Breaking Down Top Boom-or-Bust Candidates on Open Market

The 2015 NFL free-agent market is bereft of top-tier talent at the all-important quarterback position, but there are plenty of other areas teams can spend to upgrade their rosters.

Several players on the open market present particularly complicated investment propositions, though. Flashes of prior brilliance are also accompanied by durability issues, overall inconsistency or perhaps being a product of a system in some cases.

Past production and upside are strong selling points for free agents to command more money, and their prior teams face the possibility of letting them walk and starring elsewhere without any compensation in return. This is what makes NFL free agency so exciting and dramatic.

Read on for analysis on some of the standouts who will make for tricky acquisitions and are candidates to be tremendous hits or potential flops.

Jason Pierre-Paul, DE

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So Jason Pierre-Paul was on course for a third straight down season during his contract year when suddenly, over the final five games, he came to life in a big way. The dynamic pass-rusher racked up nine of his 12.5 sacks in that span.

Now the New York Giants star has that dominant stretch to go along with the 16.5 sacks he racked up in his second season as a pro, along with disappointing, injury-riddled performances. What an unenviable dilemma for general manager Jerry Reese and Co.

Another team seeking a pass-rusher could well overpay for Pierre-Paul at a price the cap-strapped Giants may not be capable of matching. The freakish athleticism and size Pierre-Paul has will only further tantalize other suitors.

Letting go of Pierre-Paul might be the best cost-effective move for New York, though. With the ninth overall pick in the 2015 NFL draft, Reese could opt to snag one of the many prospects who can rush the opposing QB.

Football Outsiders rated the Giants 22nd in run blocking this last year, so help is needed up front to balance what should be an exciting offense in 2015. It's up to New York to weigh those options and prioritize what to do with its first-round pick.

What happens with Pierre-Paul will go a long way in determining that, and if he's franchise-tagged, it will only be a feeble short-term solution to a complex, ongoing issue. It therefore stands to reason Pierre-Paul will walk.

Whoever would bring him in has to know there's considerable risk to go with Pierre-Paul's amazing talent.

C.J. Spiller, RB

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Arguably no back in the NFL has the type of mind-boggling, all-purpose-back skill set that C.J. Spiller sports. Tremendous breakaway speed, acceleration, lateral quickness, catching ability and a thick frame give him all the traits to be one of the league's best.

Spiller was certainly drafted to be among football's elite, yet 2012 was the only year he's ever been able to back up the Buffalo Bills' No. 9 overall pick in the 2010 draft.

Although it might be difficult for Spiller to convince other teams he can still be great based on his current one-year-wonder status, his physical traits speak for themselves.

Despite the diminishing value of ball-carriers in the modern NFL, at least one team should wind up paying Spiller handsomely. The question is whether Spiller will ever return to his apex form of 2012, when he ran for 1,244 yards on 6.0 yards per carry, had 43 receptions and played all 16 games.

New offensive coordinator Greg Roman pounded the rock with great success in San Francisco, though Spiller isn't as well-known for smashing between the tackles.

Dave Richard of CBSSports.com provided his take on Roman's handling of the Spiller subject in the media:

The Bills have a tough choice to make here. Their offense is still searching for a viable QB and could use someone like Spiller, provided he stays on the field. Fred Jackson turns 34 later this month and may not be back. Incumbent options include talented but fumble-prone Bryce Brown and Anthony Dixon.

Wherever Spiller goes, he seems capable of being a game-changer or quite the opposite.

While it should diminish his price tag, expectations will still be high for Spiller based on the immense potential he's never quite reached, making him a prime boom-or-bust candidate.

Jerry Hughes, DE/OLB

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Jerry Hughes appeared destined to be a first-round bust in Indianapolis but was given a new lease on NFL life in Buffalo, where he accrued 20 sacks over the past two seasons.

One can be certain that Hughes hasn't forgotten the criticism he faced, as he's proved capable of thriving as both a defensive end and outside linebacker:

But let's not forget Hughes was part of a Bills defensive front that featured Mario Williams, Kyle Williams and Marcell Dareus. That is just about as good as it gets. It helps explains why Buffalo was ranked behind only Seattle in defensive efficiency by Football Outsiders in 2014.

Then there's this statistic to share from NFL.com's Chris Wesseling, highlighting how Hughes has committed just as many penalties as sacks over the past couple of years:

Tom Reed of Cleveland.com suggests Hughes might reunite with his former Bills defensive coordinator Mike Pettine, now the head coach of the Cleveland Browns:

Indications are that Hughes wants to return to Buffalo, and why wouldn't he?

"I definitely want to be back," said Hughes in January, per BuffaloBills.com's Joe Leathersich. "You saw what we were able to do this season. The group of guys we had, to be so close, you definitely want to come back and take another shot at it, to see how we fall out to next year."

Playing with so many exceptional teammates helps the comfort level, as does the impending return of dynamic linebacker Kiko Alonso.

New head coach Rex Ryan has said he believes Hughes is an "outstanding" and "great" player. It will be interesting to see what type of money Hughes commands, because finding front-seven playmakers with his type of versatility ought to be rewarded with a sizable payday.

If the price is too much for Buffalo to pay, the team that lands Hughes will have to weigh his Bills renaissance in the context of the players who surrounded him.

It's anyone's guess as to how Hughes will fare if he's meant to be the primary quarterback harasser in the event he doesn't return to Buffalo.

Michael Crabtree, WR

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Like Spiller, Crabtree peaked in his young career with a 2012 campaign that saw him catch 85 passes for 1,105 yards and nine touchdowns.

A torn Achilles set Crabtree back in 2013 and limited him to five regular-season games. This past season, turbulence was abound in the 49ers organization, as the team missed the playoffs and coach Jim Harbaugh was essentially a lame duck.

Amid the instability, San Francisco's offense struggled, QB Colin Kaepernick didn't play great, and Crabtree lacked explosiveness after the catch, gaining just 698 yards on 68 receptions (10.3 average).

Omar Kelly of the South Florida Sun Sentinel mused about Crabtree's free-agent prospects:

Crabtree could pitch himself well with his thick frame, previously reliable hands and solid route running and imply that the circumstances with the 49ers were too difficult to show his true ability last year.

The emphasis on passing the ball is as heavy as ever in the NFL today, so Crabtree should rake in a reasonably nice sum of money. Superior open-market alternatives at his position include Demaryius Thomas and Dez Bryant, but it'd be quite a shock to see them leave Denver and Dallas respectively.

It's just tough to get a read on Crabtree and what type of receiver he'll be. Flashes in the past have indicated he can be a No. 1—look no further than the 285 yards receiving he had in three 2012 playoff games.

However, Crabtree hasn't quite gotten back to that point and could also be a mere No. 2, not meriting a huge contract. The dilemma will make negotiations tricky.

No matter what happens with the bottom-line financial details, Crabtree is going to be a boom-or-bust free agent. 

Crabtree's combination of youth (turns 28 in September) and brilliance at the height of San Francisco's recent Harbaugh heyday will give either the 49ers faithful or another NFL fanbase reason to expect the best from the enigmatic receiver.