The Boston Celtics are over the salary cap heading into free agency, which begins at midnight Sunday.

Yet, the Celtics remain one of the league’s more intriguing teams this offseason. They have draft picks — up to four in 2019, to be exact, including the Sacramento Kings’ (top-one protected), Memphis Grizzlies’ (top-eight protected) and L.A. Clippers’ (lottery protected). They have young talent. They’re financially inflexible in some ways, yet completely malleable in others.

To get a better idea of what's going on inside the Boston roster, here is a reminder of each player's contract details as we approach July 1:

(AP Photo/Winslow Townson)

Gordon Hayward

2018-19 salary: $31.2 million

Years/money remaining: three years, $98.1 million

Hayward could be under contract for up to three more years, but his deal includes a common quirk of many NBA maximum deals nowadays: there is a player option for the final season. In this case, it’s worth $34.2 million.

He can become a free agent as early as 2020 and as late as 2021. Until then, he’ll own the largest contract currently on the Celtics’ roster. Of course, there are two guys currently on the team who could garner big deals, themselves, in the coming summers.

Don't Edit

(AP Photo/Tony Dejak)

Al Horford

2018-19 salary: $28.9 million

Years/money remaining: two years, $59.1 million

For all the talk there is of point guard Kyrie Irving hitting free agency in 2019, there isn’t much about Horford doing the same, even though the big man was Boston’s best player on the way to the Eastern Conference Finals this postseason.

Many look at Horford’s max deal and wonder how he could be worth one, when better players are bringing in similar figures. In reality, most max players are actually worth more than the max. Four-time MVP LeBron James or sought-after San Antonio Spurs star Kawhi Leonard bring more to teams than their salaries imply. And they’re unquestionably better than Horford. But Horford is one of those max players who’s simply worth the salary he receives.

He has a $30.1 million player option for 2019-20. Like Hayward, he also has a 15 percent trade kicker, meaning his salary can bump up as much as 15 percent (though it can't be higher than a max contract) if he gets dealt. He’ll be 33 when free agency comes around next summer, likely with a chance to earn one, final big contract. And there’s a realistic chance he declines the option to hit the open market.

Don't Edit

(AP Photo/Charles Krupa)

Kyrie Irving

2018-19 salary: $20.1 million

Years/money remaining: two years, $41.4 million

Speaking of declining player options…

Irving is in a similar position to Horford, though there might be an even lesser chance he picks up his 2019-20 option. When Irving signed his current contract, he was able to sign for up to only 25 percent of the salary cap, and thus, his 19-20 salary is only $21.3 million.

A decently healthy Irving could command far more than that on the open market next summer, when he could sign for as much as 30 percent of a salary cap that currently projects to be about $108 million. The five-time All-Star would have to turn in a disastrous year to want the player option.

A salary that's low compared to his market value is why it also makes little for Irving to sign an extension (as he's explained before), even if he is extension-eligible. Irving can extend for up to only 120 percent of what he already makes. That would put a 2018-19 salary up to about $24 million, $8 million less than he could make in that same season if he simply signed a max deal as a free agent. Over the long term, he'd be passing up 10s of millions of dollars.

Don't Edit

(AP Photo/Ron Schwane)

Jayson Tatum

2018-19 salary: $6.7 million

Years/money remaining: three years, $24.4 million

Oh, those friendly rookie contracts. Tatum’s is the best deal the Celtics have on the books.

Like on all rookie deals, his salary isn’t even guaranteed for 2019-20 and 2020-21 with both of those years being team options that the Celtics would have to pick up in October of the previous season. Of course, they will certainly do that.

Tatum can become a restricted free agent in the summer of 2021. If he goes down the track many expect, the process will be routine. The Celtics make him a qualifying offer of $13 million. Then, they lock him up long term. Of course, they don’t even have to wait that long. The team will be able to offer him an extension prior to the 2020-21 season, and it could give him as much as the max.

Don't Edit

(AP Photo/Elise Amendola)

Marcus Morris

2018-19 salary: $5.4 million

Years/money remaining: one year, $5.4 million

With all the draft picks and reasonable contracts attached to Boston, Morris’ status gets somewhat lost. He’s not a future All-Star on a rookie deal, like Tatum or fellow wing Jaylen Brown. He’s not a current All-Star in his prime, like Horford, Hayward or Irving. He is most certainly not a draft pick. He’s simply a solid contributor sitting with a deal that pays him less than he’s worth.

Morris is fortunate his free agency comes next summer instead of this one. There will be more teams then to offer him something in line with his value. Sure, he falls in love with long 2s, but he defends multiple positions and shoots 3-pointers competently.

Part of the smarts in trading for Morris was the value he could bring not this past season but in the upcoming one. Former Celtics guard Avery Bradley, who the Celtics swung for him, will be a free agent come Sunday. Boston now has Morris for an extra year on a reasonable deal.

Don't Edit

Don't Edit

(AP Photo/Tony Dejak)

Jaylen Brown

2018-19 salary: $5.2 million

Years/money remaining: two years, $11.7 million

Brown’s situation has plenty of similarities to Tatum’s.

Both were third-overall picks, Brown in 2016 and Tatum in 2017. Of course, that means both are on similarly structured deals. It also, however, means Tatum capitalized on the first year that rookie-scale contracts increased under the new collective bargaining agreement. He makes far more than Brown does, even though Brown is one year further along in a contract that gives annual raises.

Brown can hit restricted free agency, meaning the Celtics can match any offer sheet he signs elsewhere to bring him back for an identical price, in the summer of 2020. He also becomes eligible to sign an extension, which could be worth as much as the max, before the start of the 2019-20 season.

Don't Edit

(AP Photo/Ron Schwane)

Marcus Smart

Restricted free agent

Smart is one of the more interesting free-agency cases of this offseason. The Celtics have said both privately and publicly that they'd like to keep him — doing so as recently as this week, when coach Brad Stevens told The Athletic's Jay King that he wants Smart back "for a number of reasons." And it might not be so tough.

Only about seven teams can create significant cap space this summer. Some of them, like the Chicago Bulls, will probably use the space to absorb other teams’ bad contracts, acquiring more enticing assets in the process. And considering the market is always a bit drier for restricted free agents (since teams don’t want to tie up their cap sheet for 48 hours waiting for a player’s incumbent organization to match or decline on an offer sheet), Smart could end up not making much this summer.

It means he could take a $6.1 million qualifying offer, play out next season in Boston and then become an unrestricted free agent in 2019. It means he could come back to the Celtics on a reasonable, team-friendly deal. There are hypothetical suitors that could make a sensible fit for Smart (such as the Phoenix Suns or Indiana Pacers), but signs could point most to a Boston return at least for 2018-19.

Don't Edit

(AP Photo/Ron Schwane)

Aron Baynes

Unrestricted free agent

Just like Smart, Baynes could be the victim of a tight market this summer. There are only so many spots for conventional big men. Baynes could end up with one of them, but in this game of musical chairs, someone will be left standing.

It’s why people around the league have estimated that Baynes could earn as much as the tax-payer mid-level exception, worth more than $5 million annually, but also advised he may end up having to sign a minimum deal. This market is volatile — and once roster spots, cap space and some much-needed exceptions go away, players who hope to get big deals will have to settle for less.

Baynes can go back to Boston for something more than the minimum. The Celtics have made their appreciation for him clear. But almost no matter the context, a free-agent, role-playing big man in 2018 is a wild card.

Don't Edit

(AP Photo/Michael Dwyer)

Terry Rozier

2018-19 salary: $3.1 million

Years/money remaining: one year, $3.1 million

There’s a reason 2019 is the year the Celtics roster could become dangerously expensive. Hayward will still be under contract. The team could have to hand out big money to Irving and Horford, both of whom can become free agents. It could have to deal with Smart in unrestricted free agency (or it could have just paid him in 2018). And then, there’s Rozier, who will become a restricted free agent next July, too.

Rozier could be on another team by then, depending on what happens with Irving, Smart and the rest of the roster. He could be starting on the Celtics. He could be backing up Irving, a five-time All-Star.

Maybe Rozier gets more than the mid-level exception next summer. Maybe not. It’s tough to estimate, given that 2019’s financial landscape is still forming. But there is a number of possible 2018 free agents picking up player options to enter next year’s field, which is already crowded. With the bloated, four-year contracts from 2016 still around next summer, free agency may not be so free then, either.

Don't Edit

(AP Photo/Charles Krupa)

Guerschon Yabusele

2018-19 salary: $2.7 million

Years/money remaining: three years, $10.6 million

Yabusele’s rookie-scale contract follows the same pattern as Tatum’s and Brown’s. Other than the money, though, there is one change: Yabusele just played his rookie season even though he was drafted in 2016, the same class as Brown. He spent 2016-17 in the Chinese Basketball Association and the G League.

He has three more years on his deal now — and it’s a bargain contract if the 22-year-old can work his way into the Celtics’ rotation. Like Tatum, he could become a restricted free agent in 2021, though the Celtics would be able to extend him before the 2020-21 season.

Don't Edit

Don't Edit

(AP Photo/Elise Amendola)

Shane Larkin and Greg Monroe

Unrestricted free agents

Larkin and Monroe are both unrestricted and free to sign with anyone. Larkin's return seems unlikely, given that Boston is reportedly closing in on a deal with guard Brad Wanamaker, who spent this past season playing in Turkey and could fill in behind Rozier and Irving at point guard.

Don't Edit

(AP Photo/Elise Amendola)

Semi Ojeleye and Abdel Nader

2018-19 salary: for both $1.4 million

Years/money remaining for both: three years, $4.7 million

Ojeleye and Nader had slightly differing salaries in 2017-18, but both have the exact same contract over the next three years. And they’re laid out in typical second-round pick fashion.

Each of their next two seasons is non-guaranteed. Ojeleye’s 2018-19 salary guarantees on July 15. Nader’s guarantees Aug. 1. The final year of each of their deals is a team option for $1.8 million.

Don't Edit

(AP Photo/David Zalubowski)

Daniel Theis

2018-19 salary: $1.4 million

Years/money remaining: one year, $1.4 million

Theis signed a short-term deal to come into the NBA, which means he will become a restricted free agent by next summer. His salary for this season is non-guaranteed until July 10.

--

Fred Katz covers the Celtics for MassLive.com. Follow him on Twitter: @FredKatz.