The Boston Celtics' offseason wasn't one of the busiest of the NBA, but the biggest move they made was also one of the loudest. That move was trading Marcus Smart, the longest-tenured Celtic on last year's team, in a three-team trade that saw him get moved to the Memphis Grizzlies. In return, the Celtics got back Kristaps Porzingis and a first-round pick from the Golden State Warriors that the Grizzlies acquired when they ate Andre Iguodala's salary back in the summer of 2019.

Porzingis had a nice bounce-back season with the Washington Wizards last season. It was by far the most efficient season of Porzingis' career; posting a 56.5% effective field goal percentage and 62.7% true shooting percentage while averaging 23.2 points per game. But his acquisition does bring some questions for the Celtics. How will a meh passing and playmaking team stomach the blow of losing their best facilitator? Will Boston switch as much defensively? And, a more basic question: who is Kristaps Porzingis going to start over?

Robert Williams III

Three parts of Boston's starting lineup looks to be etched in stone: Jayson Tatum, Jaylen Brown, and Derrick White. But there are three candidates for the last two starting spots, and all of them are big men. After trading for Porzingis and signing him to a two-year, $60 million extension, it would appear safe to assume that he would start as well. So that means there's one starting spot between Al Horford and Robert Williams III. Who will that go to?

It seems the odd man out is going to be Robert Williams III, who has started 81 of the last 96 regular season games he's played for the Celtics the last two seasons, for a couple of reasons. For one, head coach Joe Mazzulla prefers to have as much spacing as possible on the floor at all times. Early during last season, he echoed spacing as a priority and pillar among his coaching philosophies.

Boston ranked third in the NBA in three-point attempts per game in the regular season a year ago with 42.6 of them. Only the Golden State Warriors shot more. In the playoffs, that number dipped to 38.7 deep attempts per game. That ranked fourth in the postseason but that's a number that would've ranked fourth in the regular season. Porzingis is a career 35.9% three-point shooter, and Horford is a 37.4% sniper from deep. Williams has never made a three in his NBA career.

Another reason why Robert Williams III might be the odd man out of the starting lineup is his health. Williams has had trouble staying healthy throughout his career. Of the 390 games Boston has played ever since they drafted Williams in the 2018 Draft, Williams has played in only 209 of them. He's played at least 50 games in a regular season only twice in five seasons.

Not starting Williams would be a bit of an issue for the Celtics. Last season, according to Cleaning the Glass, the Celtics had a +8 Net Rating when he was on the floor and Al Horford wasn't. When the roles were reversed, the Celtics' Net Rating was +5.5. With Horford on the floor, the Celtics' defensive rating was 113.8. With Williams on the floor, Boston's defensive rating boosted up to 108.6. Williams' defensive presence truly makes an impact.

Williams is also by far the best finisher on the Celtics. His presence at the rim helps Boston's spacing just as much as someone else standing beyond the three-point line does.

Conclusion

But this doesn't seem to be head coach Joe Mazzula's priority. Williams played only 20.9 minutes per game in the playoffs last season, a drop from 23.2 minutes the year prior. Mazzula wants to own the perimeter and bomb away from deep. That fits more in line with Al Horford and Kristaps Porzingis' skillset.

It's debatable whether Robert Williams should start. But it seems likely that he's the odd man out of the starting lineup among this big-man triumvirate. This battle will surely be one to keep an eye on once training camp gets underway.