Hours before the start of free agency, the Vikings have gone from a relatively difficult salary cap position to a spot where they begin the league year on Wednesday afternoon with roughly $16 million in cap space.

How did that all change so quickly? It wasn't without its costs — you know about the team's decisions to release Riley Reiff and Kyle Rudolph, and the Vikings cut Shamar Stephen on Tuesday after agreeing to a two-year deal with Dalvin Tomlinson to be their new three-technique tackle. But the Vikings have also relied on some salary cap maneuvering, including a contract feature we haven't seen from them in a while, as they try to navigate the challenges that come with a veteran roster that still needs upgrades in a year where the salary cap dropped by $15.7 million.

To explain what they're up to, and what could come next, here's a set of frequently asked questions about the Vikings' cap situation:

Q: For the TL:DR crowd, how much space do the Vikings have right now?

A: They began Wednesday around $8.5 million, after Anthony Barr agreed to a restructured deal that saved the Vikings $2.9 million in cap space, but should see the number rise to around $16 million after finalizing a restructure that converts $10 million of Adam Thielen's 2021 base salary into a signing bonus, saving about $7.5 million in cap space for this season.

(A Thursday morning update to this: The Vikings' deal with Patrick Peterson counts for $9 million against the cap this year, and while Kyle Rudolph was designated as a June 1 cut — more on that in a minute — the Vikings won't realize the cap savings for that move until June. So the Vikings should be a little over $3 million until then, and would likely sign their draft class after the Rudolph move takes effect to clear $7.9 million in space for the draft class and further roster moves.)

Q: OK ... for those of us who want to go down this rabbit hole, what's with all these restructures?

A: NFL contracts are different from those in the other major North American pro sports leagues in one major respect: They're not fully guaranteed. That means teams can, and do, rework deals all the time for a number of reasons, many of which we'll cover in this post: a player is unhappy with his current deal or has outplayed his contract; a player is approaching free agency; an aging player's performance or role on the team has changed; or a team needs to create cap space for other players it wants to sign. It's no different than any contract in any business: If one party is unhappy with the terms of the current deal, it can approach the other about changing those terms. The only thing is, the other party might be more amenable to tearing up an existing contract and writing a new one in some circumstances than others.

Q: Can you give me some examples of each one?

A: Sure. The ones you hear about the most — and the ones that get celebrated the most — are when teams and players restructure a deal to add more years to their working relationship (commonly known as a contract extension). The Vikings did this with Dalvin Cook last fall because he was entering the final year of his rookie deal. It benefitted the team to have cost certainty before he got too close to free agency and could entertain offers from other teams, and it benefitted Cook to have long-term financial security before stepping foot on the field for the start of a season.

In the case of Kirk Cousins last year, the quarterback's contract had a year left and the Vikings needed to clear cap space for their other pursuits in free agency, so they worked out a new deal with the quarterback that gave him a $30 million signing bonus and actually lowered his 2020 cap hit by $10 million.

Other contract restructures, like the one Barr agreed to this week or the one Reiff signed last fall, aren't celebrated as much; they're done to reduce a player's pay for the upcoming season, usually with the implicit threat that if a player doesn't agree to the deal, he'll be traded or released.

Lastly, deals like the one that sources say the Vikings are finalizing with Thielen don't really have any effect on the player's compensation; they're just for accounting purposes.

Q: This is where I'm confused. Why is there so much talk about signing bonuses? What's so different about them?

A: So here's where teams really get creative with the cap. Signing bonuses are different from any other form of NFL compensation in two significant ways: They are fully guaranteed, and they don't hit the cap the moment they're paid. They're amortized over the life of the contract (or over five years, whichever is shorter), and hit the cap in annual installments.

Let's say Player A signs a five-year deal worth $50 million, with $20 million guaranteed, and gets five base salaries of $10 million each. Simple, right? Player A has an annual cap hit of $10 million. Now let's say Player B also signs a five-year deal worth $50 million, but gets a signing bonus of $20 million. Player B's annual cap hits would be $4 million (20 divided by 5), plus however the team and player decide to divvy up the remaining $30 million in base salaries. The team can structure those base salaries however it sees fit (provided they're at least meeting the league minimum), but the cap hit from the signing bonus doesn't change; it's $4 million every year.

Now let's say Player A and Player B are both in Year 3 of their deals; they're both underperforming, and the team is thinking about cutting each one. With Player A, it's simple: He earned $20 million in his first two years, so he's made all his guaranteed money and the team can release him without any leftover dollars hitting the cap (also known as "dead money"). If the team decides to release Player B, it has to consider a cost: There's still $12 million of Player B's bonus that hasn't hit the cap, so a release means the team would have $12 million of its cap space occupied by a player who's no longer on the team. Signing bonuses are both a way to put cash in the player's pocket right away, but they also function as a form of insurance, making teams think twice about releasing a player.

But since signing bonuses hit the cap over time, they can also be a useful tool for teams to manage short-term cap concerns. By working out a new deal that loads a fair amount of compensation onto a bonus (as the Vikings did with Cousins last year) or converting a player's salary to a signing bonus — like the Vikings have done with Eric Kendricks and Danielle Hunter in the past, and are planning to do with Thielen — the team can pay him the same amount it was originally planning to give him in cash, while spreading out the cap hit over several years.

In Thielen's case, instead of a $11.1 million salary this year, he'd take a $1.1 million salary and spread the remaining $10 million out over the final four years of his deal ($2.5 million each year). Throw in the leftover proration from his original signing bonus, $500,000 in per-game roster bonuses and a $100,000 workout bonus, and you've got a cap hit of $6 million, instead of $13.468 million.

In fact, teams have standard language written into player contracts that allows them to convert part of a player's base salary into a signing bonus at any time. Teams, in effect, can use signing bonuses to spend over the cap every year; the Vikings wrote $154.4 million in signing bonus checks from 2017-2020. If owners are willing to spend the cash to go over the cap — as the Wilfs typically have been willing to do — teams can manage their books accordingly.

Q: So why don't teams just do this with every player's salary, all the time?

A: Here's the issue: Remember the dead money thing we talked about? That's still going to hit the cap even if a player is not on the roster. Say the Vikings decide to cut Thielen before the 2023 season (ostensibly with much weeping and gnashing of teeth across the state). Under his existing deal, they'd only have a dead money charge of $1.8 million for the move, in the form of the final signing bonus proration. Under his restructured deal, the same decision, at the same time, would carry a dead money charge of $6.8 million: the $1.8 proration plus the remaining $5 million from his new deal.

Teams can designate players as a post-June 1 cut (as the Vikings did with Kyle Rudolph), which allows them to count only the current year's signing bonus against the cap, but that then pushes dead money into the future. Once the Vikings realize their cap space savings with Rudolph, they'll count just $1.45 million of dead money on their 2021 books, but will still have him occupying $2.9 million of their cap space in 2022.

Signing bonuses are basically a way to borrow from the future to pay for the present, which is why teams like the Vikings (who generally embrace a "pay as you go" structure, where dollars hit the cap at the same time they're paid out) haven't used them as much as others. In recent years, though, as they've worked on bigger deals for high-performing veterans, they've paid out bigger bonuses, creating puzzles for cap managers like Vikings vice president of football operations Rob Brzezinski to solve.

Q: What's this thing you mentioned about voided years?

A: Ah, yes — the newest wrinkle to the equation. This showed up in Dalvin Tomlinson's contract Wednesday morning, and it's not a mechanism I've seen the Vikings use in recent years. While Tomlinson will make $21 million over the next two years, the Vikings actually wrote the deal for five: the two seasons he'll play with the team, followed by three void years at the end of the deal.

In effect, that's to push part of his $12.5 million signing bonus into years where the Vikings should have fewer cap constraints (once the league's new TV deals are signed, fans are back at U.S. Bank Stadium, and some of the team's large existing contracts might not be in effect). Tomlinson will have a $7.5 million cap charge in 2023, when the final three years of the bonus hit the cap.

This is an extreme measure we've seen teams like the Raiders, Cowboys and Saints use in recent years, and the Vikings haven't done it quite in this manner. They allowed Everson Griffen to void his deal last year as part of a 2019 restructure, and voided the final two years of Barr's contract in the same fashion, but they haven't done it for players they've signed from other teams in quite some time. Their bet, essentially, is they'll be in a better position to pay the bill later.

Q: What do the Vikings plan to do with the rest of their cap space — and what if they need more?

A: They'll need the room to fill out the rest of their roster — they've only got 56 players under contract right now, and typically carry 90 in training camp — and continue their free agent pursuits for help in the secondary and on the offensive line, among other positions.

If the Vikings decide to rework Hunter's deal, addressing the defensive end's working toward his desire to be among the game's top-paid pass rushers, they could structure such a contract to actually lower his cap hit from $17.25 million in 2021. But they'd have to address their own uneasiness about reopening a player's deal with three years to go and be sure about Hunter's productivity following a herniated disc in his neck.

Safety Harrison Smith is in the final year of his deal, which is no small feat for a 10th-year safety that signed his second contract in June 2016. He has no guaranteed money left in his contract, and the Vikings are believed to be exploring a deal that could reward the 32-year-old while possibly dropping his cap number from $10.25 million this year.