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Evan Horowitz

What if Tim Duncan played for the Celtics?

Boston Celtics center Kelly Olynyk defends San Antonio Spurs power forward Tim Duncan.

Barry Chin/Globe Staff

Boston Celtics center Kelly Olynyk defends San Antonio Spurs power forward Tim Duncan.

Sunday night, Tim Duncan captured yet another NBA championship, the fifth in his storied career. Given Duncan’s remarkable success, it’s natural for Celtics fans to wonder what Duncan could’ve done in Boston. Back in 1997, the Celtics had a nearly 30 percent chance of winning the NBA lottery, which would have given them, and not the Spurs, the chance to build a dynasty around the young star.

There’s no way to know for sure how good the Celtics would’ve been with Duncan, but it is possible to make some rough estimates. Those estimates suggest that the Celtics would contended for the NBA championship from 2001-2003, but also that they would have been merely good, not great, for the majority of his career.

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A straightforward, if somewhat crude, way to figure out how a Duncan-led Celtics team would have fared is to add his annual win shares to the Celtics record and subtract the win shares of the players he’d likely replace. Win shares estimate the number of wins a player contributes to his team. An average NBA player might produce three or four win shares a season, while the best players contribute 15 or more.

During the course of his career, Duncan has averaged more than 11 win shares per season. By contrast, the Celtics often relied on a motley arrangement of big men like Travis Knight, Pervis Ellison, and Vitaly Potapenko, who combined would average about six win shares a year.

The following graph plots the projected winning percentage of a Duncan-led Celtics in red, and that of the actual Celtics in green.

Looking across Duncan’s projected career with the Celtics, we find:

■ Duncan’s biggest contributions would have come in the early years, and his value falls off considerably over time.

■ There are just two seasons where Duncan’s presence would have significantly increased the Celtics’ odds of a title. In the 2001-2002 season, instead of winning 49 games and losing to the Nets in the conference finals, they might have won as many as 58 games and secured home court advantage in that series. The year after, they could have finished first again, instead of coming in sixth.

■ When the Celtics were struggling, Duncan wouldn’t have helped much. The 2006-2007 team that won just 24 games wouldn’t have made the playoffs even with Duncan in the lineup.

■ Likewise, in the high period when Kevin Garnett, Ray Allen, and Paul Pierce made the Celtics an Eastern Conference powerhouse, Duncan’s contribution would have been minimal.

Wins (Finish)Wins (Finish)
w/ Duncan
Wins by NBA Champ
97-9836 (12th)42 (9th)62 (Bulls)
98-9919 (12th)23 (11th)37 (Spurs)
99-0035 (10th)43 (7th)67 (Lakers)
00-0136 (9th)44 (7th)56 (Lakers)
01-0249 (3rd)58 (1st)58 (Lakers)
02-0344 (6th)52 (1st)60 (Spurs)
03-0436 (8th)44 (4th)54 (Pistons)
04-0545 (3rd)49 (3rd)59 (Spurs)
05-0633 (11th)37 (10th)52 (Heat)
06-0724 (15th)31 (13th)58 (Spurs)
07-0866 (1st)67 (1st)66 (Celtics)
08-0962 (2nd)65 (2nd)65 (Lakers)
09-1050 (4th)56 (3rd)57 (Lakers)
10-1156 (3rd)59 (2nd)57 (Mavs)
11-1239 (4th)40 (4th)46 (Heat)
12-1341 (7th)45 (6th)66 (Heat)
13-1425 (12th)27 (12th)62 (Spurs)

Note: "Finish" refers to the Eastern Conference standings. The 1998-99 and 2011-12 seasons were shortened by lockouts.

Source: Basketball-Reference.com

Now, obviously, there are a lot of variables this analysis doesn’t consider. With Duncan on the team, would the Celtics still have acquired Garnett? Would they have changed their draft priorities? Could they have afforded to keep Duncan alongside Garnett, Allen, Pierce, and Rajon Rondo given the salary cap considerations? Or what if Duncan couldn’t stand the Boston winters and fled to warmer climes as a free agent.

The numbers suggest that even if Duncan had come to Boston, he probably wouldn’t have brought his five titles with him. At best, he might have helped win one or two more. And that shouldn’t really be surprising. Duncan’s championship Spurs teams included a bounty of talented players, from David Robinson to Tony Parker and Manu Ginobili, not to mention the leadership of coach Gregg Popovich.

For those Celtic fans still haunted by the question of what might have been, remember that even without Duncan the Celtics made the finals twice and took home an NBA championship. Only a handful of teams can claim to have done better over that time period.

Evan Horowitz digs through data to find information that illuminates the policy issues facing Massachusetts and the United States. He can be reached at evan.horowitz@globe.com. Follow him on Twitter @GlobeHorowitz
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