Each time the Boston Celtics send rookie James Young on a day trip to their NBA Development League affiliate in Vacationland, the announcement is met with groans from a vocal group of fans that desire to see the No. 17 pick in June's draft get an opportunity with the parent club rather than toiling for the Maine Red Claws.

It's not hard to understand their grumbles. As the Celtics navigate the second year of a rebuilding process, there's a case to be made that getting young players extended NBA minutes could expedite their development. The fact that Boston is nine games under .500 and owns an offense that has slipped to the bottom third of the league in efficiency is only additional fodder for those that leading the #FreeYoung movement.

But if there is one necessity in rebuilding, it's patience. And that virtue extends to the development of Young.

James Young possesses an exciting skill set, with the ability to finish above the rim as well as step out and hit the 3-pointer. Jim Davis/The Boston Globe/Getty Images

Celtics second-year coach Brad Stevens has glowed about Young's progress behind the scenes, particularly in the team's recent practice sessions, but an already overcrowded roster is conspiring against Young. The Celtics seem content to let the 19-year-old build confidence and work on his shortcomings under the cloak of closed practices and D-League appearances with the Red Claws, all while waiting for the appropriate time and opportunity for NBA game action.

Young scored 27 points on 9-of-14 shooting (5-of-9 beyond the 3-point arc) over 32 minutes in Maine's 137-130 win over the Delaware 87ers on Saturday. It was his second-highest scoring output of the season (he had 31 points against Fort Wayne in early December) and the Red Claws are 7-1 in Young's eight games this season.

Young's offensive proficiency is clear as he ranked in the top 10 for multiple categories in the D-League through Saturday's action, including sixth in true shooting percentage (.682), eighth in effective field goal percentage (.665), eighth in points per game (22.4), ninth in 3-point percentage (47.9 percent) and 10th in usage rate (26.5).

There is no denying Young's offensive potential. He's got a picture-perfect left-handed stroke and he punishes opponents when they let him stray beyond the arc.

But it's important to look beyond the point totals and keep in mind that the Celtics' goal is to develop Young as an all-around player. Advanced numbers suggest that he's struggled outside of basic spot-up opportunities and his defensive numbers emphasize what Young has routinely admitted: His No. 1 priority has to be developing on the defensive end of the floor.

According to Synergy Sports data, which has dissected five of Young's eight D-League appearances, he's allowing 1.065 points per play, which ranks in merely the 12th percentile among all league players. Opponents are shooting a modest 43.2 percent against him in those games, but he's been hurt by 3-point shooting.

At the NBA level, Young will be asked to guard some very skilled shooting guards and small forwards. The coaching staff has to have confidence that he can do so without being a liability.

Already crowded at the swingman spots -- even with reserve shooting guard Marcus Thornton rehabbing from a calf tear that's sidelined him the past three weeks -- there seems little reason to rush Young into what would be a limited rotation role on most nights.

Eventually, trades or injuries will loosen up the rotation and, particularly if Boston fades from playoff contention (remember, they are only 1 ½ games out of a postseason berth in a sorry Eastern Conference), then the team might be more inclined to get a longer glance at Young. But remember, too, that Stevens believes players must earn their playing time and won't simply give them minutes.

It's prudent to also recall how Avery Bradley raved about his time with Maine during his rookie season. Reps in the D-League were instrumental in him developing the confidence to perform at the NBA level. The players' situations are completely different -- Bradley was an NBA-ready defender on a playoff-caliber team who needed offensive confidence -- but there seems little harm in allowing Young to develop behind the scenes in the early portion of his NBA career. Stevens has noted that he'd rather see Young get game reps on a given night than sit on the Celtics' bench in a suit while being on the inactive list.

For now, those leading the #FreeYoung movement will have to settle for the vote of confidence that Stevens has offered in recent days.

"I think that he’s really getting better," Stevens said last week at practice, while referencing how injuries set Young back. Young missed summer league due to the effects of a pre-draft car accident, missed most of the preseason due to a hamstring injury and recently sat out two weeks with a shouder injury.

Added Stevens: "I think just continuing to string those [good] days together -- every time we go 5-on-5, if it’s for five possessions or 20 minutes, those are huge critical moments for him. And he’s taking advantage of it, especially in the last week. We’ll see how that plays itself out for playing time in the near future, but again, we have a lot of roster depth as it is right now, so we’ll see. He does add something that we could very well need in the near future, and that is the ability to play off some screens and score and make passes off screens. He’s a very fluid offensive player."

Stevens said the team views Young as more ready to guard opposing 2s than 3s, likely believing his length can mask some deficiencies. Like most rookies, Young still needs to add strength to be able to guard the typical NBA small forward.

And so expect the Maine-to-Boston shuttle to continue for Young. While he'd prefer to stick with the Celtics, he's acknowledged recently that the reps are important, saying, "It’s more of a confidence thing; get my confidence up."

Young doesn't lack for confidence. What he must remember is that his D-League assignments are as much about his coaches getting their confidence up about him.