BOSTON -- Gordon Hayward doesn't recall the specifics of the game, but he knows for sure he messed something up, probably on the defensive end. Returning to the Butler Bulldogs' bench, coach Brad Stevens was fuming at him.

Stevens slammed down his whiteboard in frustration and a piece of it shot off in Hayward's direction.

"In the heat of the game, Brad was like, 'Are you all right? Are you all right?'" Hayward recalled this summer. "And I'm like, 'Coach, don't worry about it. Let's move on.'"

Stevens obliged and quickly returned to chastising Hayward about his transgression.

The sequence offers a small glimpse into Stevens as a coach: He's demanding of his players but cares more about them as people. And no matter what sort of blip occurs, ultimately, you have to move on to the next play.

Stevens was already facing a unique challenge entering the 2017-18 season, when the Celtics brought back just four players from a 53-win team and essentially asked him to rebuild a puzzle that took four seasons of perpetual piece-shifting to construct.

Then six minutes into Boston's season-opener last week in Cleveland, Hayward fractured his ankle as he landed awkwardly after going up for an alley-oop. The team is operating under the notion that Hayward will not play again this season as he begins what Stevens has suggested is at least a five-month recovery.

With new Celtic Marcus Morris still working his way into game shape after missing the start of training camp while on trial in Arizona and Marcus Smart sidelined early in the season with an ankle injury, Stevens found himself operating with a roster in which six of his 12 available bodies were rookies.

At one point late in Tuesday's win over the New York Knicks, Stevens had a lineup of Jabari Bird (a rookie second-round pick on a G-League two-way contract), Shane Larkin (who played in Spain last season), Abdel Nader (a 2016 second-round draft pick and the G-League Rookie of the Year while stashed domestically last season), Semi Ojeleye (a 2017 second-round pick), and Daniel Theis (a 25-year-old German import this offseason) on the floor.

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All of those players, at various times, have been dispatched even when first-teamers such as Kyrie Irving and Al Horford are on the court.

Stevens has made sure to check often on Hayward, worrying more about his emotional state rather than any timeline for a return to the court. Before the shorthanded Celtics visited the Philadelphia 76ers on Friday night, Stevens phoned Hayward in his hospital room and asked if there was anything he needed to make his stay more comfortable. Hayward requested a basketball, and Stevens' wife, Tracy, delivered one before Hayward was discharged later that night.

Even down an All-Star, Stevens has been careful not to temper expectations for his Hayward-less team. Instead, he has put an even greater focus on his typical "get better each day" philosophy. While observers ponder if the Celtics can still compete for a top spot in the Eastern Conference, Stevens focuses on the the next day, the next practice, the next possession.

This season may be Stevens' biggest challenge in Boston. And yet the Celtics' biggest reason for optimism lies in the 41-year-old coach and his ability to make the most of whatever he has been given to work with.

As one rival executive told a Celtics staffer this week: "You've still got Brad, right? You'll be fine."

Despite injuries and a roster full of new faces, the Celtics aren't losing faith in Brad Stevens' ability to make all the pieces fit. Brian Babineau/NBAE via Getty Images

Stevens isn't certain of the telephone number used to reach his office at the Celtics' training facility in suburban Boston. Callers that manage to get through are greeted by a voicemail message from former coach Doc Rivers, which was recorded sometime before Stevens took over in July 2013.

"I'm just trying to coach," a shrugging Stevens said.

Since he took the job, the Celtics have demanded Stevens' full attention.

Consider this: In four-plus NBA seasons, 53 players have played a game for him, including 29 starters, according to ESPN Stats & Information. That suggests that roughly 10 percent of the entire league has played for Stevens already and rarely does a night pass when the visiting team doesn't have at least one former recent Celtic on its roster. Through four games, the Celtics have already seen six players formerly coached by Stevens in the NBA.

In his six seasons at Butler, Stevens utilized only 34 players, according to ESPN Stats & Information, and he typically knew a recruit was going to be there for four years. There were times during Boston's initial roster makeover when four weeks seemed like an extended stay.

This summer's roster teardown was still jarring because of the high cost to import the star talent that president of basketball operations Danny Ainge believed necessary for the Celtics to truly return to title contention. Even in landing Hayward, Boston had to wave goodbye to mainstays such as Kelly Olynyk and Avery Bradley in order to generate cap space. Trading for Irving came at the price of two starters, including a top-five MVP candidate in Isaiah Thomas.

That left Boston dangerously young at the end of its roster. Stevens had hoped to lean on his more established players in the early stages of the season, but injuries have thus far prevented that. The Celtics, with an average age of 25.06 years, are the fifth-youngest team, according to the NBA's roster survey conducted at the start of the season, trailing only the Suns (24.49), 76ers (24.65), Lakers (24.89) and Trail Blazers (24.89).

To combat his team from getting caught up in its overall lack of experience, Stevens won't allow his players to use age as a crutch.

"Let's beat the age thing. Let's not talk about the age thing," Stevens said. "Let's talk about how we can be better at what we can control and how we can learn and grow every day and everybody expedite the learning curve."

Added Stevens: "If we're not committed to getting better, individually and collectively, then we're not good enough. If we are, we'll see what happens. But that's the only way to go about that."

AP Photo/Charles Krupa

Irving had heard the hype about Stevens from afar and was naturally curious when they crossed paths at the 2017 All-Star Game in New Orleans. While Stevens had downplayed the idea of coaching an All-Star Game -- noting his team's regular-season success simply got him a good seat for the high-scoring exhibition -- he utilized the opportunity to remind the players involved just how much they meant to those watching.

In the moments before tipoff, Stevens played a video that his film staff put together that included highlights and photos of the East All-Stars when they were kids.

"I get asked all the time about what inspired you to get into coaching and what inspired you to want to do this. And the truth of the matter is nobody's inspired to get into coaching," Stevens said in his pregame speech to the Eastern Conference stars.

"It just means you weren't good enough to be playing. Ultimately, the people that inspired me as a kid were the Reggie Millers, were the Larry Birds, were the Magic Johnsons, the Michael Jordans of our era. The guys that were sitting in your shoes. So I just want to say thank you to you for the opportunity to share the day with you. And, also, I recognize the fact of what you mean to those kids."

Irving was floored. It was his fourth All-Star Game but says it was his most memorable. He has become even more smitten with Stevens since the August trade that delivered him to Boston.

"Individually, I think Brad just stands out in his own way," Irving said. "He's an intellectual coach, he's an understanding coach, in terms of his knowledge of the game and what he wants from his players and how to best get the most out of his players on a day-to-day basis.

"And to have a coach like that, it's pretty great. I've had a lot of great coaches in my career and understanding the transition of going from one coach to the other, they all bring something different to the table. For me, coming into a whole new environment and for Brad to integrate me well into the culture of Boston and what he's established here, he made it a lot easier for me."

Irving has full confidence that Stevens will figure out how to best put all these puzzle pieces together.

"When he establishes [players' roles] and when he's explaining that everyone has to be great in their role and collectively have to be great -- every single detail is important, every person is important. And he makes sure he relays that message to every single one of us every day.

"It's pretty easy to kinda buy into what we're trying to accomplish after that."

Stevens turned 41 on Sunday. The Celtics had a rare off day and Stevens joked it likely spared him from having to hear his throng of rookies sing another off-key rendition of "Happy Birthday."

Stevens is still the third-youngest coach in the NBA, trailing only the Los Angeles Lakers' Luke Walton (37) and the Cleveland Cavaliers' Tyronn Lue (40). What's maybe more startling is that, in his fifth season, Stevens is tied for the sixth-longest tenure among NBA coaches with their current teams (an honor he shares with Atlanta's Mike Budenholzer, Charlotte's Steve Clifford, LA Clippers' Doc Rivers and Philadelphia's Brett Brown).

It's fair to wonder if the Celtics can compete without Hayward. Stevens may be a wizard but history suggests that young rosters don't make it far in the postseason.

Excluding the NBA's first season, no team has ever reached the NBA Finals while playing five rookies in the playoffs, according to Elias Sports Bureau. In fact, the last team to make the conference/division finals with that many rookies was the 1962-63 St. Louis Hawks, who utilized six rookies in the postseason.

Sure, the Celtics might not be leaning on five rookies by the postseason, but they are right now. Jayson Tatum, the No. 3 pick in June's draft, has looked sensational and Jaylen Brown, the No. 3 pick in the 2016 draft, appears to have made a big leap forward as well. They are the silver linings in the immediate aftermath of Hayward's injury, especially while Irving finds his way in Boston.

Getting a couple of healthy Marcuses (Smart and Morris) will give the Celtics the sort of experience and talent to be competitive on a nightly basis. Even while playing shorthanded, Boston hung with both the Cavaliers and Bucks early this season before giving up late leads.

Celtics players are putting their full faith in Stevens and his one-day-at-a-time approach.

"[Stevens] said in the locker room the other day: 'We don't even have to be on the right page, just as long as we're on the same page,'" Brown said. "So everybody is just trying to get on the same page and get everybody moving to the same accord, and I think we'll be fine."