As in life, nothing in free agency is guaranteed.
Some free agents are relatively safe bets, players who are pretty much a lock to perform as advertised. This is not an exploration of those players. Rather, the list below consists of 10 of the biggest boom-or-bust propositions set to be on the market.
These 10 players carry sky-high potential -- and the risk that they could fall far short of expectations. For all of them, I've sketched out what will happen if they boom and what will happen if they bust. I've also picked a team that is ideally situated to take the risk of signing each guy.
NOTE: Ages listed reflect how old each player will be at the beginning of the 2021 NFL season, on Sept. 9.
The boom scenario: Peterson consistently provides the same type of sticky man-to-man coverage that enabled him to hold Seahawks receiver DK Metcalf to one catch for 6 yards on four targets, per Next Gen Stats, in Arizona's Week 7 overtime win over Seattle. (Metcalf finished the game with two total catches for 23 yards.)
The bust scenario: In his 11th NFL season, Peterson's speed drops to the point that he becomes a liability rather than an asset when matched against the other team's WR1.
Who should take the risk? San Francisco 49ers. With four cornerbacks (Richard Sherman, Jason Verrett, K'Waun Williams, Ahkello Witherspoon) headed for free agency, San Francisco will need fresh blood in the secondary. (UPDATE: The 49ers are re-signing Verrett to a one-year deal, per NFL Network Insider Ian Rapoport.) As the Niners did with Sherman when he left Seattle, they can still get good football and veteran leadership out of Peterson, who will surely enjoy having two chances per year to stick it to the Cardinals, should Arizona decide not to shell out dough to keep him.
The boom scenario: Fournette picks up right where he left off in the playoffs (448 yards from scrimmage and four total touchdowns in four postseason games), further reestablishing himself as a premier NFL running back after resurrecting his career with the Tampa Bay Buccaneers.
The bust scenario: That super-productive stretch aside, Fournette fails to learn from the mistakes that brought his time with the Jaguars to a messy end. "Playoff Lenny" disappears like a mirage.
Who should take the risk? Atlanta Falcons. Arthur Smith landed Atlanta's head-coaching job largely because of the success he had as the offensive coordinator in Tennessee, where he funneled his attack through running back Derrick Henry. Fournette has the skills to fill a Henry-like role and is even better than Henry as a receiver out of the backfield. The Falcons face major cap issues, but there might not be a huge market for Fournette in a glutted position group that also includes free agents Kenyan Drake, Chris Carson and Marlon Mack.
The boom scenario: Carson rebounds from his subpar, injury-hampered 2020, regaining the form that made him one of the NFL's most productive running backs with the Seahawks in 2018 and '19, when he recorded 2,381 rushing yards (fifth-most in the NFL in that span) and 16 rushing touchdowns.
The bust scenario: The injury issues that have kept him from starting all 16 games in any of his four pro seasons thus far continue to get in his way. He's also likely to have trouble if he ends up on a team with an offensive line that struggles in run-blocking.
Who should take the risk? Miami Dolphins. At 5-11 and 220 pounds, Carson is better suited to fill the role of power back that Jordan Howard was ticketed for before being released by Miami last November, and Carson could be especially effective in a rotation with Salvon Ahmed and Myles Gaskin. Carson -- who doesn't turn 27 until Sept. 16 -- showed the Dolphins firsthand what he's capable of in Week 4 last season, when he rushed for two TDs and produced 100 yards from scrimmage in a Seahawks win.
The boom scenario: Fuller shows that, when healthy, he is one of the NFL's most dangerous wide receivers, especially in the vertical passing game.
The bust scenario: Injuries once again get the best of a player who has missed 25 games over the past four seasons with the Texans.
Who should take the risk? Washington Football Team. Washington might not have a quarterback yet, but pairing Fuller with Terry McLaurin would give that person a lethal one-two punch to work with.
The boom scenario: Smith-Schuster -- who is still just 24 -- makes everyone forget about his underwhelming last two seasons with the Steelers, looking more like the player who became the youngest in NFL history to hit the 2,500-yard receiving mark early in '19.
The bust scenario: He signs somewhere with the expectation of producing like a No. 1 receiver but plays like a No. 2, re-enacting what happened when he was asked to step up after Antonio Brown's exit from Pittsburgh two seasons ago.
Who should take the risk? New England Patriots. Some might wonder if a player who made a habit out of posting TikTok videos of himself dancing on opponents' logos would be a good culture fit with Bill Belichick's Patriots, but this team desperately needs the kind of help at receiver that Smith-Schuster could immediately provide.
The boom scenario: Hendrickson continues to build upon his stunning fourth-year breakout, in which he logged 15 starts and 13.5 sacks, eclipsing his previous highs in both categories (three starts, 4.5 sacks) by a wide margin.
The bust scenario: Isolated from the circumstances that helped him thrive in 2020, Hendrickson struggles to replicate his 2020 success, suggesting his production last season had more to do with the surrounding talent on New Orleans' top-four defense -- specifically, from playing opposite one of the NFL's top defensive ends (Cameron Jordan).
Who should take the risk? Las Vegas Raiders. The defense that finished 29th in the NFL in sacks last season could use some serious pass-rushing help. New defensive coordinator Gus Bradley plants Hendrickson opposite Maxx Crosby, casting them as the cornerstones of what he wants to build up front.
The boom scenario: Ngakoue -- who doesn't turn 26 until later this month -- brings the same kind of pressure that helped him record at least eight sacks and double-digit QB hits in each of his first five NFL seasons.
The bust scenario: Asked to do too much against the run, where he is sometimes overmatched at 6-foot-2 and 246 pounds, he struggles -- and those issues outweigh his pass-rush production.
Who should take the risk? Cleveland Browns. Cleveland reportedly tried to land Ngakoue last year, when he was traded from the Jaguars to the Vikings. Signing him away from Baltimore would hurt an AFC North rival AND provide a complementary pass-rushing force opposite Myles Garrett, with Olivier Vernon, who served that role in 2020, headed for free agency himself.
The boom scenario: Tomlinson continues to provide the same steady play that resulted in two consecutive seasons of 49 tackles and 3.5 sacks.
The bust scenario: He is signed by a team that wants him to be a disruptive pass-rusher, but that kind of transformation probably isn't in the cards for the run-stuffing behemoth, and he falls short of expectations.
Who should take the risk? Jacksonville Jaguars. Though Tomlinson doesn't have the potential to affect opposing quarterbacks in the same way that pending free agent Larry Ogunjobi does, he is more consistent overall and would instantly upgrade a Jaguars defense crying out for interior help after ranking 30th against the run in 2020.
The boom scenario: Fully recovered from the torn Achilles that ruined his 2020 season, Mack showcases the form that led him to rush for 1,999 yards and 17 touchdowns in 2018-19.
The bust scenario: Mack becomes another unfortunate example of a young running back derailed by serious injury.
Who should take the risk? New York Jets. Frank Gore, who led the team in rushing at 37 years old last season, is gone, and there's no certain replacement waiting in the wings. If the Jets trade Sam Darnold and draft a new quarterback at No. 2 overall, acquiring Mack to lead a strong running game would go a long way toward giving the new rookie signal-caller a chance to find his sea legs.
The boom scenario: After seven years with the Packers, the All-Pro center picks up right where he left off last season, serving as a stabilizing veteran force up front.
The bust scenario: The risk here is relatively low, but Linsley did lose time with a knee injury last season, and he is entering his age-30 season. I don't personally think this will prove to be the case, but it's conceivable that he begins the decline phase of his career next season, which would represent a disappointment for whichever team pays top dollar to land him.
Who should take the risk? Cincinnati Bengals. Trey Hopkins could shift to right guard (where he started 12 times in 2017) to make room for one of the NFL's great centers, giving the Bengals another avenue for beefing up Joe Burrow's protection (in addition to the fifth overall pick in the 2021 NFL Draft).
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