ORLANDO — The well-worn maxim of summer league play is this: It’s not possible to tell who can play for real in the NBA, but it is possible to tell who can’t. Through three games, there have been few surprise for the Celtics  and that’s not necessarily a bad thing.
Jared Sullinger is a good basketball player, who will compensate for his lack of athleticism with smart play and strong skills. E’Twaun Moore  is confidently taking the reins of the team. Fab Melo is active, but raw. Kris Joseph has good skills across the board. JaJuan Johnson  has remained an enigma, but he started to hit his stride in the second half of their third game on Wednesday, an 85-77 win over the Pacers.
The good news thus far is that each of them has flashed an NBA skill, but obvious questions remain. Here’s a thumbnail look at each prospect:
The raw numbers are decent — 14.7 points, 8.7 rebounds and 11-for-12 from the free throw line — but what has really stood about Sullinger’s game is his feel for rebounding and his ability to pass out of double teams. While concerns about his less-than-ideal physique are legitimate, he’s been able to compensate with his skills, which are numerous.
“He’s a great passer, good rebounder, always in the right position as far as rebounding the ball,” C’s coach Ty Lue said. “He’s going to be good for us.”
Sullinger went 7-for-12 from the floor against the Pacers, operating mostly out of the low post where he is clearly comfortable. The Celtics have not had back-to-the-basket presence like Sullinger since the glory days of Leon Powe , but where Powe was intent on bulling his way to the basket, Sullinger has been able to read the play and make the appropriate pass.
“Getting double-teamed for the majority of your life, you’ve got to learn how to pass,” Sullinger said. “If you didn’t know how to pass, I wouldn’t be here right now.”
He has also shown a knack for getting to rebounds, something that is a major need for the Celtics. At the moment, he’s clearly the most NBA-ready of their roster players this summer.
The question: How much will his lack of athleticism hinder him against NBA competition?
Sullinger has proven he can play at a high level in high school, college and now here in summer league. The larger test awaits.
The Celtics arrived as a group about 20 minutes before the 11 a.m. tipoff while the Pacers were already on the floor getting warmed up. Moore made his way out to the court with about five minutes to spare, but was once again in his element when it began. Over the last two games, he’s made almost half his shots and continues to run the offense as well as can be expected and with few turnovers.
“He has a calmness about him,” Lue said. “Never sped up, never in a hurry. Sometimes I think he tries to play the point guard role so much that he’s not being aggressive.”
Moore has consistently scored 15 points a game with a solid 2-1 assist to turnover ratio. His contract situation is explained here, but he has looked like an NBA player throughout the week.
The question: Is he a point, a two or something in between?
Moore isn’t concerned about the distinction. “To me, it doesn’t matter,” he said. “That’s the great thing. I can play both, on the ball or off the ball. Wherever someone needs me, just be ready.”
Like his star-crossed rookie season, Johnson has alternated between tentative play and moments of obvious skill. He started slowly — again — and then caught fire in the fourth quarter, scoring seven of his 11 points and making all three of his attempts.
Even more than Melo, Johnson is the biggest mystery of the summer. The talent is there, but he has yet to put it together in consistent stretches and there is the ever-present issue of his thin frame. Johnson was pushed off the block repeatedly, but when he moved into a face-up game, his long-range jumper was on the mark.
The question: Will Johnson be able to play a meaningful role this season?
The Celtics know he can score. What they want to see is whether he can defend and run the court. His natural position is also up for debate. There’s been some talk of trying him at small forward, but he’s played the four most of his career. Again, reading too much into a handful of summer league games is never a good idea, but Johnson still has much to prove.
Melo can block shots, he plays hard on defense and he has a limited offensive game that is essentially limited to dunks and put-backs. The Celtics knew all that when they drafted him and they understand that he will require lots of work.
Here’s the revelation: He can pass. Melo recorded three assists, including one in transition and one off a dribble-drive (seriously). He also threw an outlet pass right to a Pacer and airmailed a skip pass to a surprised Joseph, who happened tp be sitting on the bench. “That would have been a good pass,” Joseph said. “Had I been in the game.”
“We just have to get him to value the ball more,” Lue said. “He’ll throw the ball anywhere. He don’t care. He’s a great guy and he’s a hard worker, so he’ll pick it up.”
The free-flowing nature of summer league may not be the best environment for a player like Melo, who is still learning the game. Lue thinks that getting around Kevin Garnett  will be good for him. For now, the Celtics are being patient.
The question: Will Melo be able to get on the court this season?
Right now he’s the backup center, but the Celtics will look to add another veteran big man, either with the bi-annual exception or a minimum contract. Players have earned minutes with less ability than Melo, but he has a long way to go.
The second-round pick has impressed with his ability to score and his 12 points and seven rebounds on Wednesday were both highs this week. The Celtics think he can play both wing positions and for a team that carried Marquis Daniels  and Sasha Pavlovic  last season, any infusion of talent is welcome.
“He’s playing defense, he’s rebounding, he’s attacking,” Lue said. “He’s playing really good for us and that how we want him to continue to play.”
The key for Joseph is remaining aggressive at all times. He won’t have the luxury of easing himself into games in the NBA and he’ll have to expand his range out to the 3-point line. The transition from leading scorer in college to bench player in the pros isn’t an easy transition, but Joseph has flashed the requisite skill level.
The question: Will he remain on the roster?
Joseph signed a two-year deal for the minimum and neither year is guaranteed. He’ll have to prove himself at all times if he is to get a second contract. It may be out of his hands, ultimately. The Celtics are still scrambling to complete the roster and if he loses out in a numbers game, the cost is basically nothing. His job is to make that decision as difficult as possible.