WALTHAM — During his time with Sacramento, Marcus Thornton was able to see first-hand the halo of talent that Kings big man DeMarcus Cousins carried with him — as well as the trouble that always seemed to dim it.
Cousins was a top five pick with a create-a-player’s size (6 feet 11 inches, 270 pounds) and skill set: He could shoot, he was a bruiser on the glass, and he had the kind of post moves that looked as if they came from a class in creative movement.
But he also had a reputation — some of it earned, some not — for being mercurial and difficult to coach.
Now, as a fifth-year veteran, Cousins leads the Kings in scoring (24.7 points per game), rebounding (12.3), and blocks (1.6) and is third in the league in player efficiency rating. Thornton, like many around the league, can see his growth as a player.
“He changed a lot,” said Thornton, whose Celtics face the Kings in a New Year’s Eve matinee Wednesday at TD Garden. “Now he’s starting to trust his teammates a lot. When he was younger, I guess he felt like he could do everything by himself. Now he’s starting to trust his teammates, and that’s made him a better player.”
Cousins’s ability was never in question, Thornton said. His maturity was.
“He’s very competitive,” Thornton said. “You mix that with him being young, it happens sometimes. But you can’t deny what he does on the court. It’s crazy sometimes. I saw it first-hand.”
Cousins has refined his repertoire, sharpening his outside shooting and becoming even more of a force in the paint.
“He’s a load,” said Celtics coach Brad Stevens. “He can play. I watched a game the other day where he hit six or seven 18- to 20-foot shots that I think he was more inconsistent with in the past but very capable. But now he’s good at them and it just adds a whole other dynamic to the team.”
As a big man, Celtics forward Jared Sullinger keeps tabs on what Cousins is doing.
“He’s one talented big man,” Sullinger said. “He does it all — passing, shooting, he scores in a variety of ways.”
Sullinger took note of the effect that playing for USA Basketball over the summer in the World Cup had on Cousins.
“I just think his leadership this year from the previous years is totally different,” said Sullinger. “Everybody used to claim he was a hothead. He’s down for his teammates, I know that much. I think Team USA really helped him out.”
Thornton said he and Cousins spoke a lot over the summer about the USA Basketball experience.
“It’s just him maturing,” Thornton said. “I think the USA thing helped him a lot. Now he knows what it’s like to be not that guy. They had a lot of players for USA, so now he knows how his teammates feel. So now he’s going out there and he’s playing great.”
Sullinger is probable
Although he was still limited in practice Tuesday because of a twisted ankle, Sullinger is probable for Wednesday’s game.
“I think it’s just a matter of how he progresses, how he feels, what the trainers say, everything taken into account,” Stevens said.
Sullinger landed on another player’s foot fighting for a rebound Saturday against the Wizards. He has played in all 28 games this season and said he wouldn’t want the ankle to be the reason he sat out for the first time.
“I don’t like missing time,” Sullinger said. “And every day is valuable for our development, especially us being so young.
“I’ve played through so many injuries before. So health is not really an issue for me. I think it’s just an injury where you work out, you play, you ice it, and do it all again tomorrow.”
Thornton, who has been out since Dec. 15 with a torn calf, practiced again Tuesday, but his status for Wednesday is uncertain.
“I’m tired of sitting out,” Thornton said. “So hopefully I can [play]. It’s always frustrating to sit out and watch the team go through times like this.”
Smart or Nelson?
Marcus Smart has started three of the four games since the Celtics traded Rajon Rondo, but Stevens is still deciding whether to keep it that way or to start Jameer Nelson, who was in the starting five against the Magic on Dec. 23. The question he’s trying to answer, he said, is: “Who really complements one another? We’re continuing to look at it and I don’t think there’s a clear-cut answer, but we’ve got to create a clear-cut answer and then go with that.” . . . A statistic that could be telling Wednesday: Over their last three games, the Celtics are last in the league in first-quarter scoring. The Kings are third.
Julian Benbow can be reached at firstname.lastname@example.org.