Baynes and Morris are two completely different players, but both are fighting for the same spot. Baynes, a big brutalizing center, is the Celtics best rebounder. With that being the Celtics biggest weakness as well as one of Al Horford shortcomings, it gives Baynes a clear path to being put in as the Celtics starting center in the Amir Johnson role, allowing Al Horford to slide to the 4.
Baynes is stronger, taller, a better rebounder, and a better rim protector than Morris. If you look at there per 36 minutes stats, Baynes blows Morris away in all the categories the Celtics were bad in last year. Baynes has averaged over 10 rebounds per 36 minutes in every year of his career other than his rookie year, while Morris has never even averaged over 7 by the same metric. Baynes has also averages 1.1 blocks per 36 for his career, while Morris is just at 0.3. Morris is too small to guard centers which would mean while playing alongside Al Horford, Al would be the one guarding the opposing team's center. Al has made clear that he does not want to do that. Morris doesn’t solve any of the Celtics problems there. On top of that, Baynes has already shown the ability to shoot consistently from mid range this preseason, which bodes well for a Celtics team that loves as much spacing as it can get. Nonetheless, Morris stretches defenses far more effectively than Baynes will.
Morris is a far better all around offensive player. In Morris lineups the Celtics can have 5 shooters who can stretch the defense to the 3 point line at all times. He’ll be better at switching onto smaller players on screens than Baynes and is a great on ball defender. Baynes, 31, has only started 24 games in his entire career and started a total of 3 in the last 2 years, whereas Morris has started 218 games in his career and 159 in the last 2 years. Baynes also has a fouling problem. He’s had only one season where he averaged LESS than 5 fouls per 36 minutes, in which he averaged 4.4. Morris is far more use to starting and playing heavy minutes and is far less foul prone than Baynes. Morris would allow the Celtics to play faster and be loaded above average athletes at every position. While Morris hurts the rebounding numbers significantly, he may make the Celtics nearly unguardable.
The Celtics could end up mixing and matching at the bigman spot opposite Horford depending on the matchup, however we expected them to do that last season and Amir Johnson ended up starting 77 of the 80 games he played in during the regular season. While Brad has hinted at saying the Celtics may decide to change their lineup based on matchups, he made no clear indication that that’s what they intend to do.
Jayson Tatum, who started the Celtics last preseason game, could also have his name thrown in the ring if he plays well enough, but that will all depend on how comfortable he is playing small ball 4 as a rookie small forward who is just getting his feet wet in the NBA. Morris, Tatum, and Baynes are all extremely different players. A lot of the Celtics style of play will be defined by which one they decide to run with.
With all that said, Baynes should be the one who gets the majority of the starts this season. It can’t be overstated how agonizing it was to watch the Celtics get repeatedly killed on the glass game after game last season. It seemed like if they could just rebound they would be a serious challenge for Cleveland. Baynes can help that and if he continues to knock down the mid range jumper the way he has so far, he spaces the floor enough that he isn’t a complete offensive liability. It’s not as if Amir Johnson was Karl Malone out there either. Having 1 player in a lineup with Irving, Brown, Hayward, and Horford that isn’t a real offensive threat isn’t going to kill them. Morris will be great in small ball lineups, but running him out there with his weak rebounding numbers too often might only make the Celtics rebounding problems even worse than they already were. Opening night might be a night for Morris if Cleveland runs with a James-Crowder-Love frontcourt as they’re threatening to do, but for the majority of the season it should be Baynes.