Early adversity forcing young Boston Celtics to rise to occasion

* Tonight on TNT: Celtics at Bucks (8 ET)

Here’s something not often associated with the NBA’s most traditional franchise: A behind-the-head dunk that ignited Boston fans much the same as a Larry Bird 3-pointer used to do. The new explosiveness was showcased by Jaylen Brown, who celebrated his 21st birthday Tuesday with an opening-quarter slam against the winless Knicks.

Brown (23 points on 16 shots) and rookie Jayson Tatum (22 on 15) became the Celtics’ first duo to score at least 20 points in the same game before their 22nd birthday.

“They are young guys,” said Celtics coach Brad Stevens, “but to us, with the situation we’re in, they’re guys. Like, we need them to be guys. We need them to play well on Thursday.”

On Thursday, the Celtics (2-2 after their 110-89 clobbering of New York) will be on the road for a rematch with the Bucks (3-1), who beat them 108-100 in Boston’s home opener last week. Brown (18.8 points) and Tatum (14.8) rank No. 2 and 3, respectively, in points and minutes, while helping to fill in for All-Star Gordon Hayward, who appears to be out for the season after suffering a gruesome ankle on opening night in Cleveland.

“We’re in a situation right now where we’re going to expect a lot out of those guys and we need them to be great, we need them to be able to respond to adversity, and we need to be able to respond to pats on the back just the same,” Stevens said. “We have high expectations for them; they should have high expectations for themselves, and they’re getting a great opportunity. So, we need them to continue to be good, and there’s a lot of fun in that, I think.”

As much as they miss Hayward and wish he were here, the Celtics remain a team of upside. Apart from Al Horford (31) and Aron Baynes (30), everyone on the roster is 25 or younger. At this early-season moment, the Celtics are defined more by Brown and Tatum than they are by Kyrie Irving, their All-NBA point guard who was acquired from the Cavaliers last summer.

“It’s very obvious,” said Horford of the Celtics’ inexperience. “We feel it, we see it out there. Even though we have a lot of younger guys, they’re mature beyond their years. It’s not like you’re dealing with the rookie headaches and things like that. But you can really tell it’s game four of the year and we still have a ways to go.”

We don’t need them to do anything they don’t do well. We just need them to be good at what they do well.”

Brad Stevens on rookie Jayson Tatum and second-year player Jaylen Brown.

Hayward’s abrupt absence has changed the point of view without altering the ultimate goal.

The Celtics still want to contend for championships. In the absence of Hayward, however, they can’t afford to reach for that outcome in the here and now — not with so much to be learned and proved.

Will they be a defense-first team? An up-tempo, share-the-ball team? Those have been traits of Stevens’ preceding four seasons in Boston. But it’s too early to predict the future for this developing roster.

Irving is averaging 20 points and shooting 37.5 percent as he adapts to his new surroundings. He is going to be judged by whether he can take pressure off his young teammates even as he pushes them to thrive ahead of schedule — a passive-aggressive tack that LeBron James utilized while leading Irving and his fellow Cavaliers to The 2015 NBA Finals in their first season together.

The young Celtic most likely to flourish is Brown, the second-year swingman (and No. 3 pick of the 2016 Draft) who generated 25 points on opening night while overcoming the shock of Hayward’s gruesome injury. Brown has high hopes for himself across the board — his long-term goals include serving as president of the NBA Players Association — but Horford doesn’t want to see him trying to take on too much too soon.

“We just need him to do what he’s been doing,” Horford said. “He has that capability to be a great defender but also impact the offensive end. We want him to keep developing, to keep growing and improving, and make sure that we’re staying after him and he starts understanding how we want him to play. He’s been doing a good job of that.”

Though he has quickly become Boston’s No. 2 scoring option, the Celtics are encouraging Brown to look beyond the numbers.

“It should happen naturally,” said Horford of Brown’s statistical growth. “There’ll be some nights that he’ll have high-scoring games. There’ll be other nights that he’ll be doing more defensive work. I think it’s impressive because there’s not a lot of guys like him that are able to play defense and offense. He’s usually guarding one of the better guys defensively, and at the same time we’re expecting him to score the ball.”

Tatum, the No. 3 pick last June, has been encouraged by teammates and coaches to hoist up shots.

“That’s the toughest part, me being a rookie and being out there with Al and Kyrie – instinctively I think, just give them the ball, even though I may be open,” said 19-year-old Tatum, who has also emerged as Boston’s No. 3 rebounder (7.8). “But it’s good for our team, when somebody’s open, to shoot their shot.”

The Celtics opened the second quarter Tuesday with a second-unit lineup meant to force-feed Tatum. Over the next 4:25 he sandwiched a pair of 3-pointers around a fade away, a transition assist, and a block that he turned into a full-sprint alley-oop as Boston stretched its lead out to 20 points.

Tatum, who was 1-for-5 from the arc through his first three games, hit 4 of 6 on Tuesday. In the first half alone, he and Brown combined for 30 points – three fewer than the Knicks.

“We don’t need them to do anything they don’t do well,” Stevens said. “We just need them to be good at what they do well.”

As Brown continues to invest in the details of his development – extra shooting, weightlifting, individual skills workouts and the like – he serves as an inspiring role model for Tatum.

I’m really conscious of talking to the (new) guys and making sure they understand where they need to be, and that they feel comfortable with what we need to do.”

Al Horford, on quarterbacking the Celtics’ defense

“In Jaylen’s case last year, he played really well, and he did what he did really well and he kept going — (but) there were times when he didn’t,” Stevens said. “And I thought the best thing about him was how he just responded regardless. He was great working to get better the next day, regardless of whether the game before had gone well or not. That’s the one thing we can take from that experience that Jayson needs to copy.”

They’re not the only Celtics hoping for big steps. Fourth-year guard Marcus Smart has been sidelined the last two games by a sprained ankle, but after losing 20 pounds over the summer there is promise of him fulfilling his potential as a hardcore defender while achieving consistency at the other end — just in time for him to cash in as a restricted free agent next summer. Forward Marcus Morris, recovering from knee soreness, may make his Boston debut by Halloween, while backup point guard Terry Rozier has already shown that he can fit into a variety of lineups.

“With Gordon’s loss, our help is going to come from our bench and our depth — from guys like (rookie forward) Semi Ojeyele and once Marcus Morris gets back,” Horford said. “Guys like that are going to be able to step in and help us fill that void, which is hard to do when you have one of your best players out.”

Hayward’s injury forced Stevens to simplify the offense. He was investing in cohesion by keeping his starters together on the court until 4:20 remained in their blowout win against the Knicks.

“We just need to do what we’re doing better,” Stevens said. “Our defense is going to have to be really, really good as we grow and learn how to score the ball together.”

The defensive principles haven’t changed.

“It’s very similar to last year,” said Horford. “I’m really conscious of talking to the (new) guys and making sure they understand where they need to be, and that they feel comfortable with what we need to do.”

When Brown came out with 2:41 left, a group of fans behind the basket shouted happy birthday to him. He waved to them from the sideline. It’s early in his career, but he was already feeling at home.

Ian Thomsen has covered the NBA since 2000. You can e-mail him here, find his archive here or follow him on Twitter.

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