Jared Sullinger wasn’t happy.
“I was so frustrated by everything,” the second-year Celtics forward said recently.
It showed on the court, where his temper boiled over.
“That’s when he got all these flagrant fouls,” said Satch Sullinger, Jared’s father. “It was because he had to act it out in some way.”
And over the course of two nights in early January, Jared was whistled for three flagrant fouls, including two within a span of 24 seconds in a 129-98 loss at Denver Jan. 7.
Watching from his home in Columbus, Ohio, Satch knew something was wrong.
“I know body language when I see it,” said Satch, who coached Jared at Northland High School in Columbus. “I know my sons. There’s a look that maybe you won’t see, but I know it. And it was frustration. I knew that wasn’t my son.”
Satch said he knew he couldn’t just call or send a text message. Instead, he traveled to Boston, attended several practices and games, and sat down with Jared.
“I’d love to give you the advice that he really gave me,” Jared said with a laugh, “but I’d get fined really, really, really, really bad.”
So he was stern?
“He was really, really stern,” Jared said. “He was really aggressive. He just let me know what he sees and kind of told me, ‘This is not you and this is not what got you here. This is what’s going to get you out of here.’ ”
The two watched game film and Satch pointed out his son’s poor body language.
“He didn’t worry about moves,” Jared said. “He didn’t worry about shots. He didn’t worry about defensive stuff. He just said, ‘Look at your body, look at your attitude, look at your alertness. It just seems like you’re not in the game.’ ”
Satch recalled telling Jared, “When you get to this level, your skills don’t diminish. They don’t disappear. What happens is, the most important inches are the 6 between your ears. That’s where the attitude and the effort come in at. You have to learn to control those.”
Sullinger worked at it — and since his last flagrant foul in a 111-105 loss to the Clippers Jan. 8, he has come a long way.
He was averaging 12.8 points and 7.2 rebounds while posting seven double-doubles in 34 appearances before that foul.
But in 21 appearances since, Jared is averaging 13.6 points and 10.0 rebounds while having posted 12 double-doubles, including six in a row at one point.
He had a monster game of 25 points and 20 rebounds Jan. 15 against Toronto, making him the first Celtic to have a 20-20 game since Kevin Garnett in 2007.
Sullinger also poured in a career-high 31 points along with grabbing 16 rebounds in a Feb. 7 win against Sacramento.
His performance against the Kings was sandwiched between two other double-double outings that earned Sullinger Eastern Conference Player of the Week honors for games played Feb. 3-9. During that three-game stretch, Sullinger averaged 20.3 points, 12.7 rebounds, and 1.7 blocks.
And after many of his big games, Jared credited Satch’s advice for helping him turn around his season.
“That talk really helped me out,” he said recently.
Looking back, Sullinger, who is shaking off the rust after missing three games because of a concussion, said his flagrant fouls were the flashpoint of his frustration.
“I kept holding onto things, kept arguing that it wasn’t a flagrant foul,” he said. “It was tough at that time.”
Said Celtics coach Brad Stevens, “We probably didn’t do a good enough job after the first two or three of saying, ‘Hey, this is what’s considered a flagrant. You can’t do that anymore.’ ”
The two talked, and, Stevens said, “He’s still playing physically, but there’s a difference between playing physically and playing flagrant. He’s made that adjustment appropriately.”
From afar, Satch has been impressed with and happy for his son.
“Well, as a dad, it makes me feel proud that my sons still let me be dad,” Satch said. “They know that I don’t have a handout. Everything that I suggest to them doesn’t benefit me; it benefits them. Everything I tell them is for their good and they trust me with that, so they listen.
“I’m also not just a dad that watched my son play. I made a living in this game for 34 years before I retired. I have knowledge of the game.”
Utah Jazz guard Trey Burke, who played for Satch in high school and is a childhood friend of Jared, agreed with Satch on that point.
“Coach Sullinger, he’s one of the guys that is always going to have a quote for you or a life lesson for you,” Burke said. “He’s a great teacher. That’s the No. 1 thing that I can say about him. He knows how to teach the game of basketball and life lessons.”
Jared said he’s thankful for those lessons.
“Honestly, I’m lucky to have someone like my father in my life because any other father would just be like, ‘You know what? Collect your paycheck. Be happy,’ ” Sullinger said.
“But no, my father wants me to do it for the right reasons, for the right ways, and to pay my respects to the game of basketball because it was here before I was born, it’s going to be here when I’m dead and gone. I’ve just got to pay all my respects.”
It’s not as though young players won’t struggle from time to time, Satch said.
“I think all of them go through it,” Satch said. “Some of them work through it without the support. And Jared, he has the support. I’m not a dad who just showed up the other day. I’ve been there from day one. There’s a relationship there.
“There’s a bond that’s still there and will always be there.”Baxter Holmes can be reached at Baxter.Holmes@globe.com. Follow him on Twitter @baxterholmes.