Will Robert Williams or Al Horford Start for the Celtics?

The Celtics begin training camp in two weeks featuring one of the more quietly interesting starting lineup battles across the NBA, though not as flashy as the Chris Paul debate in the bay.

Joe Mazzulla announced Derrick White will start at point guard, Kristaps Porziņģis arrives next to Jaylen Brown and Jayson Tatum as shoo-ins, leaving one spot for past starting lineup mainstays in Robert Williams III and Al Horford. Choosing between the future five in Rob, and Boston’s both past and recent rock in Horford, presents an immediate challenge for Mazzulla.

Brad Stevens made traded Marcus Smart to shift excess depth from the guard position to center, considering injuries and age limiting Williams III and Horford during last season. That creates the assumption those three players will become easier to manage than the three starting-level guards proved last year. While no decision has been made on who starts between Williams III and Horford entering camp, Williams III enters as the favorite.

The desire to accelerate Williams’ involvement among the team’s other young cornerstone players, to create a captivating defensive tandem between shot-blockers, while alleviating the massive load the team placed on Horford, 37, likely makes the job Williams III’s to lose as opening night approaches. Though the luxury of having depth and matching up against different opponents remains, making that choice will become easier said than done for a team that has looked to Horford as its two-way veteran staple.

Williams III deferred to Horford and White when his play formed a case to start him following his return from surgery to play successfully in a limited role off the bench. White sat in the playoffs when Williams reimerged. Horford, meanwhile, last came off the bench in his first game back with the Celtics, a preseason exhibition against the Raptors that showed him the challenge of entering cold off the bench. Outside of five games with the Hawks and seven with the 76ers in 2019-20, Horford started for the entirety of his career, even going back to Florida where he started 98-of-109 contests.

“For me, as a competitor, I want to be in a position that I’m playing when it matters most, but I do like to start,” Horford said in 2021. “That’s just the reality, me as a competitor, me liking to feel like I can contribute and a great asset. Yeah … (I do want to start).”

Horford maintains a strong case to continue starting two years after reclaiming that job in Boston, despite logging over 5,000 minutes in two seasons since, climbing to 89th all-time. His familiarity with Brown and Tatum stems back to 2017 while Williams III’s only sporadically developed over the past five years. Horford brings more to the table in the half court offensively, making his game more flexible alongside Porziņģis’ as a three-point and mid-range shooter who can pass comfortably above the arc, from the high post and with his back to the basket. Horford also sets better screens on and off the ball than Williams III, and posted 1.17 points per possession in his rare rolls to the basket last year (58th percentile). His limitations at the basket offset playing with Porziņģis.

What the Celtics hope for in starting Williams III — despite those offensive disadvantages compared to Horford — is growth next to playmakers. Going back to his first action in 2019-20, Boston’s offense blossomed during Williams III’s minutes, ranking third among the team’s regulars (113.4 offensive rating, 115.4 with Tatum) in 2022.

Injuries and inconsistent involvement dropped him beneath Horford last year, along with their lineup usages, but his offensive rating still improved to 116.3 (120.3 with Tatum) by getting Boston into transition through stops, turning offensive rebounds into scores and finishing 74.7% of his shots as a lob threat. Still, Rob’s unselfishness sometimes went too far, more likely to pass than shoot. Spacing becomes a challenge after he rolls or if he can’t.

“I don’t care if I play two or 20 (minutes),” Williams III told CLNS Media during the east finals. “As long as we get the dub.”

Williams III, when encouraged, shared the sentiment of teammates who stressed how important he could become to the offense. A double-double with 13 points and 15 rebounds against the Hawks in Game 4 showed him sealing smaller opponents, taking more field goal and free throw attempts (11 combined). Too often, teammates ignored him on rolls, he stood around in the dunker’s spot or set ineffective screens that couldn’t create advantages.

Williams III didn’t utilize his jump shot last season, Mazzulla urged against doing so after he hit one in Philadelphia and Rob’s passing became a smaller part of the offense. That followed an injury-riddled offseason and missing most of the first half of last year. Training camp next month provides a fresh start.

Horford and Williams III both provide compelling arguments defensively. Starting Williams gives Boston two shot-blockers, Porziņģis statistically playing some of the best pick-and-roll defense in basketball with the Wizards last season and Williams III hedging off the opponent’s worst offensive player to provide inside help.

That argument goes hand-in-hand against benching him, since he’d need to play drop instead of that help defense as the lone big on the floor, not the best use of his strengths, especially isolated against stronger centers. Horford, while a weaker rebounder and rim protecter, can guard the pick-and-roll and let Porziņģis play back while switching screens along the perimeter, in line with how Boston defended in its 2022 double-big alignment.

Mazzulla will have to try both and switch back-and-forth as injuries and rest inevitably change how the Celtics look to start games. He hopes to retain some of the team’s small ball identity too, pulling Malcolm Brogdon and the team’s backup wings into this conversation when debating who the fifth member of the team’s closing lineup should be. Porziņģis played both high against the pick-and-roll and dropped with Washington, and can do all the above offensively.

Who starts doesn’t matter significantly. Horford should probably play fewer minutes this year overall while Williams III ramping-up his playing time becomes a must at this important part of his career. Horford’s defensive versatility and physicality must persist off the bench though. Williams already proved capable of thriving in bench bursts, and managing his minutes could keep him healthier too. Rob also needs to roll to score, which would limit Porziņģis’ time inside the arc. The Celtics need to cut in that case, or he’ll find himself shooting almost exclusively threes, like Horford.

“We can take some pressure off of Al and Rob … we can continue to use Kristaps in the same way we used Al … with his ability to play out of the post, I think that’ll take some pressure off our guys and give a different dimension to our offense … the pairings work well,” Mazzulla said in June. “You can play Al and Kristaps, you can play Kristaps and Rob, and we’ll continue to play Al and Rob.”

Given the Celtics’ sparse bench scoring, occasional issues with offensive stagnancy and the coach’s fixation on floor spacing, Horford carries a compelling case offensively to give Porziņģis more flexibility. The defensive possibilities between Rob and Porziņģis appear tantalizing. Both need to play consistently to achieve them. We’ll find out soon which direction Mazzulla will lean.

Either way — double big is back.