If you're like me, you've been celebrating the arrival of Al Horford so much that you may have forgotten that the Celtics have their first summer league game tomorrow (July 4th) at 7 p.m. We'll get our first taste of rookie Jaylen Brown as he goes up against the Sixers and number-one pick Ben Simmons. However, this Celtics summer league team is filled with storylines beyond this year's lottery pick. Let's delve into some of the things to watch.

Who's actually on the team?

*Via RealGM

Who has the most to prove?

Besides for the second-round picks who are on non-guaranteed deals, James Young will really need to show some tangible improvements this season. Though Young will be one of the first to remind you that he's still one of the youngest guys on the team, his lack of development has been troubling, and the Celtics are not in a place as a team that has time to keep non-productive players on the roster. Young did a great job working on his body last season, but he still looked a step too slow defensively, and he was never really trusted enough to do anything offensively except stand in the corner. Young will need to prove that he can be a consistent knockdown shooter and someone who Stevens can trust defensively. But even then, there might just not be a place on the roster for him.

Returning player to keep an eye on?

The trio of R.J. Hunter, Terry Rozier, and Jordan Mickey will be very interesting to watch. All three may at some point be dependable members of the rotation, and all have shown promising signs in their development. Hunter will need to demonstrate that he's strong enough to guard bigger perimeter guys and that he can be a consistent shooter. Rozier will need to have a better command of the game as a point guard. Last season he impressed with a better-than-expected jump shot and an uncanny ability to rebound despite being 6'0". With his elite athleticism, Rozier could be nearly unguardable running the pick and roll in a summer league setting. As for Mickey, fans are intrigued by what he can be in theory: a slightly undersized big who is an elite athlete that can protect the rim, switch on the perimeter, and hit threes. If Mickey shows he can do all of that, there's a very real chance that he could find himself being the first big off the bench this season barring any veteran additions.

What to expect from this year's first-round picks?

Jaylen Brown and Guerschon Yabusele are two intriguing prospects. Both are big,strong, and athletic wings that have skills tailor-made for breakout summer league performances. Yabusele has gotten praise from the Celtics coaching staff for his lateral quickness and passing ability, so it'll be interesting to see how those traits look in a professional setting. Though his three-point shooting looks like a strength based on last season, he's previously been a low-30% shooter who's been wildly inconsistent, so we shouldn't expect him to come in and be a knockdown shooter. However, if he does show off an impressive shooting display to go along with versatile defense and strong passing, the Celtics might seriously consider keeping him in the states where they can keep a watchful eye on his development.

Brown on the other hand will be in a direct position with the sophomore wings for potential rotation minutes. His passing and defending will be interesting to watch. Brown has been pegged as a "no feel" player because of his constant efforts to try and force plays on a Cal team that had no spacing. However, when in transition he has shown vision and advanced passing ability that should be in display a lot during the summer league. It'll also be interesting to see his jump shot progression, which, according to teams that worked him out, has looked pretty good. Brown could potentially play an Andre Iguodala type role as a Swiss army knife forward that can help the flow of the offense and defend some of the best wings. It'll be interesting to watch his level of competitiveness against various prospects during the summer league. Will he be as locked in against Dionte Christmas as he will be against Ben Simmons? That could be a telling sign to his motor.

When are the games?

Here's a rundown of the schedule:

Be sure to come to CelticsBlog for all the latest recaps and news regarding the summer league!