I find advanced stats very interesting, because they tell a story. It's up to us to unravel that story, but that's not what I'm going to try (in detail). I'm just going to put out some observations about combo's that seem to work and which not so much (according to advanced stats, just read this sentence with everything I post here). Maybe it helps with the puzzle how our (starting) line ups should look like. These stats are from all 24 games (decent sample).

Defensive ratings (DR)

Defense is hard to evaluate and defensive ratings definitely aren't perfect in doing so, but here are some things that stand out (pure defensively speaking). Both Theis and Ojeleye have been terrific on the defensive side with a DR of 88 and 89. That they mostly play against other bench units, which are less effective might be a factor.

Rozier has a 95 DR. In fact Rozier and Theis show up on all the best defensive combo's. Their excellent REB% may have something to do with that. Another player who does very well is Baynes (97 DR). On the other hand Morris is the worst defender and it really doesn't matter with whom he plays (106 DR). Horford and Irving don't have ratings to write home about either (103 DR). Where in Horford's case it's remarkable that he's in all the units that do a very poor job on the boards and he's in noone of the line ups who do average or better in that regard.

What's interesting is to compare how new line ups combo's are doing. Firstly Irving/Smart (104 DR) is not doing better on defense than Irving/Brown (103 DR), offense is a different matter though. Horford/Morris is terrible as only bigs defensively. Tatum and Hayward both are better partners for Horford and limited minutes strongly suggest (both 76 DR with Al) that Baynes or Theis would make a great improvement on that end.

If we look at line up combo's of 3/4/5 players we see that Rozier/Smart together are in those best defensive line ups. Irving hardly shows up on those units, unless he's covered by Rozier or Baynes. Apart from Morris and Irving it's Brown who pops up on the least performing rotations. That's a bit weird considering his defensive reputation.

Offensive ratings (OR)

Leader in offensive rating is Irving (110 OR) quickly followed by Morris (109 OR). These guys are fantastic on offense. Tatum scores best of the rest (107 OR). The guys that are out of tone on the offensive end are respectively Ojeleye (102 OR), Brown (100 OR) and Rozier (99 OR). Sometimes the eye test does suffice. What it mostly comes down to is bad shooting, since these 3 players all shoot 48 TS% which is also by far the lowest on the team.

The next question is which players play good together. Irving/Smart scores a high 112 OR, maybe Kyrie benefits from Marcus' playmaking? Line ups with Smart do well in the AST/TO department. Irving with Baynes 110 OR is also a good combination, we've seen some pick-and-roll action between them. Obviously combo's of excellent offensive players (Irving, Morris, Tatum) are high on the list, but Hayward is also a name that always comes forward in efficient units.

Hayward doesn't go well with Brown though (94 OR). Rozier together with Horford seems like a recipe for disaster for some reason (89 OR), while Rozier and Theis do seem to share a connection on the floor (105 OR). Almost every unit performs very well as long as Rozier or Brown isn't in it. Harshly said.

Net ratings (NR)

In general we can say that Theis and Ojeleye have done a formidable job so far in and against secondary units with spectacular net ratings of 15 and 13.

Hayward is a very interesting part of that, since he's able to elevate limited offensive players to great heights. That aspect could make him the perfect candidate to lead the bench unit as he's doing right now. To show you, see below for offensive improvements (while the defensive doesn't suffer) when those guys are individually playing together with Hayward:

Theis 104 => 113 (+ 9 OR)
Ojeleye 102 => 110 (+ 8 OR)
Smart 106 => 109 (+ 3 OR)
Baynes 105 => 106 (+1 OR)

The player who has been poor on both ends of the court has been Brown. He actually is the only guy with a negative NR (-1). Other players who should improve are Horford (rebounding), Morris (defensively) and Rozier (offensively).

While in general Morris and Horford are not a great combo, they oddly enough do play together as solely bigs in an extremely good closing unit (Irving/Hayward/Tatum/Morris/Horford). They have a NR of 35. Having 5 shooters/scorers on the floor may pay dividends when the game is on the line.

Conclusions

• Jaylen Brown has been dragging the starters down a lot. Probably best to let him get back to his old self in the second unit for now. He has to shoot a lot better.
• Gordon Hayward has been playing better than I thought. But he's doing so well with running the second unit it would be a shame to break that up. Like one said, it doesn't matter who starts the game but who finishes it.
• Marcus Morris had a fantastic start of the season, but he has been cooling off in the last 8 games. He's not a great fit with Horford in general. It's probably better to start Baynes with Horford.
• Terry Rozier is a very strange guard. His rebounding rate is excellent and also his overall defense, but most players suffer from playing with him. Maybe he has to be more team orientated on offense?
• Not much news to tell about Kyrie Irving, Jayson Tatum or Marcus Smart. The stats show us exactly what kind of players they are on the court. The combo Irving/Smart is a nice find.
• Daniel Theis and Semi Ojeleye have been excellent in the minutes they've gotten. An increase of minutes for Theis should be contemplated (only 11,9 MPG)
• After all these conclusions there rolls out a remarkable potential starting 5. Since those 5 players haven't played a single minute together on the court this season. Namely: Irving/Smart/Tatum/Horford/Baynes.