That's why Brad, and probably Joe and most of the league, don't really put players into those boxes anymore. It's hard to pigeonhole them. Is he a small forward? Or a shooting guard? But he can't dribble the ball so he can't be a guard. He's too small to be a big...etc. They just see them in the buckets that Brad articulated back in 2017:
Less to do with their size and more with what they actually do on the court...and so some of the "positions" a player plays may change during a game. Tatum might be the sole ball handler in a lineup, in another he might be the big. In any lineup you may have two ball handlers (White and Jrue), two wings (the Jays) and a big (KP), you may have two ball handlers, (White, Jrue) a wing (Tatum) and two bigs (Al and KP), the same lineup but where Al plays more like a wing and defends wings so it would be one ball handler, two wings and a big, or one with no big at all.
Ever since I heard that from Brad back in 2017 I tried to look at the players and positions through his lens...that's why I just see Hauser as a wing. He plays on the wing, off the ball, comes off screens, defends other wings. It's hard though because most of us are all old and grew up on the PG/SG/SF/PF/C designations 
This is a pretty good summary, and I don't disagree with the highest level classification of ball handlers (or combo guards), wings, and bigs. But as the second part of the post says, there is easily at least one more layer of nuance to each of these. Combo guards can lean more point guard type (1) or be the true hybrid guard type (1/2). Wings can be more guard wings or small wings (2/3) or be more forward/big wings (3/4). And bigs can be hybrid 4/5 (like Horford) or just straight centers/5 like Kornet.
I feel that this classification within the basic 3 categories also misses a classification for the 3/4 or swing. A player that can play as both a wing and a small PF, but probably isn't a true big. Tatum fits this. If you had to pick one of the basic 3 categories, I would call him a wing, he is certainly not a big. But he is a 3/4 swing, not a 2/3 wing. I see that many teams now play a swing in the core line up (Tatum, Harris, Siakam, Aaron Gordon, Durant, LeBron).
Here is how I would group the current Celtics:
Combo: Holiday, White, Pritchard, Springer, Scheierman
Wings: Tatum, Brown, Hauser, Walsh
Bigs: Porzingis, Horford, Kornet, Tillman, Queta
I am not sure if Scheirman is more combo guard or wing. It seems like we have more combo guards or ball handlers than we need. We have 5 bigs, but the group tends to lean more 5 than 4. Of our wings, Tatum is the only real swing (3/4) type. That swing 3/4 role is a littel light to me but overall, the roster is well balanced.
