Paul Pierce was chatting on the sideline at TD Garden this week when he was bear-hugged from behind.

“Aaaaah,” said the Celtic legend in mock pain. “Who is this, Danny? This feels like Danny.”

“Because I’m so strong,” said Ainge.

There was much laughter between the two before the Celts went out and scored a comeback win over Milwaukee. And there seems to be a lot of that around the club these days.

Pierce gave a nod to the new atmosphere in the absence of Kyrie Irving.

“I mean, everybody knows that,” he said. “I’m not even in the building yet, and I’m hearing every day that everybody feels like a weight’s been lifted off of them.

“Just walking around, you can tell. Or just seeing it on the court. It’s different.”

Another different thing Pierce is seeing on the court is a better approach from Jayson Tatum. Pierce told the Herald last season that Tatum needed to get to the hoop — and, thus, the free throw line — more to increase his production. Through four games, Tatum’s scoring average and free throw attempts has both increased from last year.

Pierce even offered to come in and tutor Tatum, who said he read the story and would welcome the assistance. Coach Brad Stevens also said he’d gladly accept such help from No. 34 in the rafters.

Pierce has yet to school the third-year Celt, but he believes his points have gotten across.

“I think he heard me,” said Pierce. “I mean, he knows what he has to do, man. He’s smart. He knows what he has to do to take the next step. He’s got to get to the basket more and get to the free throw line more, and I think he’ll have more opportunity this year.”

Speaking of opportunities, Pierce is getting ready to give another NFL team a shot at his affection. He’s spoken about switching his allegiance from the Patriots to the Rams, who will next year be moving into a spectacular new stadium across the street from The Forum in Inglewood, Pierce’s old stomping grounds.

“Yeah, I was going to stay with the Patriots until (Tom) Brady retires, but I think, because it’s my hometown, I’m going to have to switch to the Rams once they move into Inglewood,” Pierce said. “That’s home. Once they move into that new stadium in Inglewood, I’m with the Rams.

“Who knows if Brady is going to be playing next year anyway? I hope he is, but who knows?”

As for the Rams’ new home, Pierce said, “Man, that stadium is really nice. The whole community is changing. It’s good.”

Until the move, he has his comeback prepared when people out there give him a hard time for supporting the Pats.

“Listen, I grew up without a football team in L.A.,” Pierce said. “There was no football team in my childhood in L.A., so it’s an easy explanation when people ask me why I’m a Patriots fan.”

Focus on defense

Stevens didn’t realize all the issues that would plague the Celtics last season, but coming into the year, he was, in fact, worried about how his club would be on defense. And that appears to be an issue for the Bucks, who gave up an average of 117.5 points in their first four games after surrendering 109.3 last year.

It’s obviously an unfairly small sample size, but after the loss to the Celts Wednesday, players were quietly saying there has been slippage on that end of the floor.

Stevens has told the Herald in 2018, “Well, I think you always have concerns that, you know, for us, we’ve played two straight seasons eight months all the way ’til late May. It’s not like playing into the Finals, like people talk about, but it’s pretty close. And the idea that when you have a team back that was so good defensively that we don’t skip steps, I’d say that’s the No. 1 concern I’ve got. I’ve watched teams before have really good years and then kind of go through the motions on that end of the court. And we can’t do that.”

But they did. After giving up 100.4 a game in 2017-18, the Celts allowed 108.0 last year.

Bucks coach Mike Budenholzer is hoping to avoid a hangover from winning 60 last season. He’d been through it before in Atlanta, hitting 60 in 2014-15 and getting swept by Cleveland in the conference finals, then going 48-34 and being broomed by the Cavs in the second round the next year.

“It’s certainly a great experience for me personally as a coach and to just kind of understand hopefully what kind of focus coming into this year, objectives and handling the season and working your way through the season,” Budenholzer said. “With players, I would say this group’s focus has been really good, and I think they’re very ready for this season and this challenge. And hopefully as a coach you learn and hopefully I’m better and we don’t regress.”

Celtics timeline

Tuesday at Cleveland, 7 p.m. — It might be fair to say the Cavaliers are ahead of expectations, in that, you know, they’ve won a couple of games heading into the weekend. The key has been big man Tristan Thompson averaging a double-double. The Celtics beat the Cavs by 46 and 23 points in two preseason meetings last month, but it’s important to note that Thompson didn’t play in either of those games. At the start of a three-game road trip, it’ll be important for the Celts, well-rested after being off since meeting the Knicks on Friday, to come out hard and tuck this one away.

Thursday at Charlotte, 8 p.m. — The big story here will be Kemba Walker’s return to Charlotte after playing his first eight seasons there. He can expect to be greeted warmly, in that his public stance was that he wanted to stay with the Hornets as a free agent, but the club didn’t want to pony up the money. This will also be a big game for former Celtic Terry Rozier, who went in the opposite direction over the summer and will be looking to make a mark with the home crowd against their former hero.

Saturday at San Antonio, 5 p.m. — A little different start time for a Saturday game (4 p.m. Texas time), but the same old Spurs. The roster changes, but Gregg Popovich’s club rolls along. The big challenge for the Celtics here will be inside (as it will be on most nights). LaMarcus Aldridge is 6-10, and while he can step outside and score, he’ll be a particular problem nearer the bucket.