Boston Celtics Rookies Got a True NBA Test in Their First Summer League Loss

it's one thing to be drafted, meet a bunch of new teammates, and try to play well, but it's another to do it during a brutal stretch of schedule in the middle of a desert playground

Las Vegas, NV — Celtics rookie Chris Cenac Jr. takes a free throw during a summer league game on July 13, 2026 | John Karalis

LAS VEGAS — Summer league is supposed to be the first taste of NBA life for newly drafted rookies. Guys are getting an early taste of the next level, figuring out the speed and physicality, the coaching, and the officiating, all while trying to work on the first tweaks to their games. 

But for Boston Celtics rookies Chris Cenac Jr. and Dillon Mitchell, Monday’s game against the Atlanta Hawks gave them a taste of one of the NBA’s tougher tests: The third game in four nights. 

“Some of us aren’t used to it,” Mitchell said with a laugh. “[It’s] just about coming out with the right energy, the right mindset … just a learning lesson.” 

Playing in the NBA can be a grind. An 82-game schedule is constantly debated for being too long, and stretches like this can test even the best players and guys who have been around for a while. The fatigue was clear with Cenac Jr., who led the team with 16 points, but also five turnovers in the 102-90 loss.

“Gotta push through,” Cenac Jr., a man of few words, said after the game. “Gotta go out there and compete.” 

Head coach Amile Jefferson put some of that onus on himself. The energy of the game changed when some fresh legs at the end of the bench checked into the game. But he also wanted the heavier usage guys like Cenac Jr. and Mitchell to feel the challenge and bust through it.

“Sometimes things don't go your way. Sometimes you can't make a shot. And at the end of the day, can you lean on your habits and on the effort and on competitive spirit?” Jefferson said. “When it's not going well, can you just find ways to make a play? And is that a deflection? Is it a steal? Is it an offensive rebound? I tell all our guys every day: everyone can offensive rebound. Everyone can sprint the floor. Everyone can play defense. So, just trying to keep the guys in the right mindset.” 

Jefferson was definitely putting the effort in with his coaching. On top of the constant communication with his players, he smartly called a late first-half timeout to set up a two-for-one opportunity before halftime. Even down big towards the end of the game, he challenged a play and won. 

“I keep saying, it's a great growth experience for me, and so it's a good time to learn the rules, know what you can and can't do, how you can use timeouts to your advantage,” he said. “For me, just find ways to get better and help these guys develop and hopefully reach their dreams.”

The Hawks were resting their top draft picks, but the Celtics struggled to get out of their own way sometimes. Some of Cenac’s turnovers were clearly the result of mental lapses. One Celtic threw a pass directly off another teammate’s face. And there were plenty of passes thrown to empty spots where one player expected one thing, and the other was on a different page. 

Summer league is a tough environment for guys whose heads are probably still spinning from the draft process. The lack of practice time and continuity is a challenge in itself, and then the league plops everyone in a desert playground full of parties, events, and countless ways to get into trouble. Cramming three games into four days is truly an early test of discipline and focus. 

They had their moments, but neither guy played great. But this game isn’t really the test. It’s what comes next, and how they handle this next game, and the next tough bit of scheduling, that will show their team what they're made of. 

“Just making sure you're in shape, making sure you're ready for the next game,” Mitchell said of the lesson learned. “Just coming out with the right mindset. Make sure you get your sleep. Just everything that goes goes around with it.”