Sources: Grant Williams heading to the Mavs in signing and trading

Dallas Mavericks and restricted free forward Grant Williams are finalizing a four-year, $53 million contract as part of a three-team signing and trade agreement with the Boston Celtics and San Antonio Spurs, sources told ESPN Adrian Wojnarowski on Wednesday.

Sources said San Antonio will receive forward Reggie Bullock and an unprotected first-round trade in 2030 from Dallas, while the Celtics — Williams’ former team — and the Mavericks will each receive two second-round draft picks.

The Celtics will also receive a $6.2 million trade exception, according to ESPN’s Bobby Marks.

Getting Williams, a 24-year-old who averaged 8.1 points and 4.6 rebounds off the bench with the Celtics last season while shooting 39.5 percent from 3-point range on 3.7 attempts per game, gives Dallas a young and versatile 3 -and- a D forward who should be the perfect complement to the Mavericks’ star-studded backcourt from Luka Doncic and Kyrie Irving.

And by acquiring Williams in a tag and trade, Dallas can still reach the full middle-level exception, giving him an option to add another important piece in free agency. Sources tell ESPN’s Tim McMahon that Dallas has an interest in Portland Trail Blazers offensive lineman Matthys Thibul.

Williams, the 22nd pick in the 2019 NBA draft from the University of Tennessee, has been a key part of Boston’s runs to the NBA Finals and Eastern Conference Finals each of the past two seasons. While he’s vacillated on and off coaching Joe Mazzola at times this season, he’s back in a senior role off the bench as the playoffs continue this year, just as he did a year ago under Emi Udoka when Boston went to the NBA Finals. For the first time since 2010.

Having become much more expensive this season with the acquisition of Kristaps Porzingis from the Washington Wizards last month in a deal that saw franchise franchise Marcus Smart move to Memphis, Boston opted to acquire other second-round draft picks rather than match a deal to keep Williams as part of his roster next season. , when the Celtics should once again be one of the top contenders in the East.

Williams, with his ability to guard above his 6-foot-6 frame and drop an open three-hit, has been one of the more prolific restricted free agents on the market this summer, especially for opposing teams. He’s a career shooting percentage of 43% on three-point corner throws, compared to 34% on all other three-point attempts, according to ESPN’s stats and information group, and he’s a versatile defensive player who guards a variety of opposing players.

The Mavericks are now hoping they can fulfill a similar role as Dallas hopes to bounce back from last season’s disappointing 11th-place finish in the West, which saw the Mavericks fail to even qualify for Championship Play.

Williams underwent surgery on his left (non-shooting) hand after the season, but the Celtics said he was expected to be ready in time for training camp.

It was a busy season for the Mavericks, who re-signed Irving to a 3-year deal, made two overnight trades to round out a pair of first-round picks – center Derek Lively and forward Olivier Maxence-Prosper – and signed guard Seth Curry.

Meanwhile, San Antonio reaches the salary cap with the acquisition of Bullock, a 38-percent 3-point linebacker, as well as landing another potential future draft asset in the first round swap.