Jump shooters are just 16 for 51 from behind the three-point line against Boston Celtics forward Jaylen Brown this season. (AP Photo/Wilfredo Lee)

The Boston Celtics season got off to a rough start. They lost all-star forward Gordon Hayward on opening night and quickly dropped to 0-2 after matchups against the Cleveland Cavilers and Milwaukee Bucks. Since, however, the team regrouped and won 12 straight — the first NBA team to do so after an 0-2 start — and are now a league-best 12-2.

So how has Coach Brad Stevens managed to keep the momentum going despite the loss of Hayward in addition to injuries to fellow all-stars Al Horford and Kyrie Irving? By having a historically good defense.

The Celtics are allowing a league-low 97.5 points per 100 possessions which, if sustained, would be the eighth-best defensive effort since 1979-80, the year the NBA adopted the three-point line. It’s also nine points better than the average team, which is on par with some of the best defensive Boston teams of all time.

Season Points allowed per 100 possessions Team’s defensive rating relative to the league (lower is better) Playoff result
1963-64 83.8 -10.8 Won Finals
1964-65 84.2 -9.4 Won Finals
2017-18 97.5 -9.0 ?
2007-08 98.9 -8.6 Won Finals
1961-62 85.1 -8.5 Won Finals
1962-63 87.4 -8.5 Won Finals
1960-61 84.5 -7.6 Won Finals

A key component of this suffocating defense is their opponents’ lack of success from behind the three-point line. Teams are shooting 32.1 percent against them on three-point attempts, significantly lower than the league average (36 percent). Typically, you would think success like this would be fleeting or a by-product of a small sample size of games, but consider this is only slightly better than what we have seen against Boston since Stevens took over as head coach — opponents have a bottom-five three-point percentage against the Celtics in every season since 2013-14 — and it starts to look sustainable for the season.

Another factor: Jaylen Brown and rookie Jayson Tatum have thrived in larger roles with Hayward out for the season and Horford and Irving missing time.

Brown, the third overall pick in 2016, has been good at stopping spot-up shooters (46.2 effective field goal against) and limiting the options of the ballhandler on the pick and roll (34.3 eFG percent against), placing him in the top 35 percent of all NBA players against these play types. He’s also leading the team in contested three-point shots per game (3.6), which has limited jump shooters to 16 for 51 shooting (31.4 percent) from behind the arc, the 10th best mark among players defending at least 50 three-point jump shots this season.

Tatum, the third overall pick this summer, is contesting 2.9 three-point shots per game and has held spot-up shooters to 0.71 points per possession and a 38.9 eFG percent against, which ranks No. 2 and No. 3 overall, respectively, this season among defenders tasked with stopping at least 40 such plays. He has allowed the ballhandler on the pick and roll to score just 0.53 points per possession against him, good enough to place him in the top 10 percent of the NBA’s defenders. Being a stout defender is not new for Tatum — he ranked 67th among 1,025 Division I players for points allowed per possession as a freshman at Duke in 2016-17.

With both Tatum and Brown on the court, opponents are shooting 31.5 percent from three-point range in addition to scoring just 97.5 points per 100 possessions, in line with how the 3-10 Sacramento Kings are performing on offense this season. When joined on the court by Horford, Irving and Aron Baynes, teams are averaging 90.3 points per 100 possessions against the Celtics, with Boston producing a net rating of plus-14.1, the same net efficiency seen from the 2017-18 Golden State Warriors.

It’s unlikely the Celtics continue on a 70-win pace, but based on their points scored and allowed we would expect them to have an 11-3 record, a one-win difference from their actual results to date. If we regress their record to account for the small sample size of 14 games, we can expect Boston to win 57 games, its best season since 2008-09 and five wins more than expected by the Detroit Pistons, giving the Celtics the No. 1 seed in the East by season’s end.

Eastern Conference Projected wins in 2017
Boston Celtics 57
Detroit Pistons 52
Washington Wizards 46
Toronto Raptors 44
Orlando Magic 44
Philadelphia 76ers 43
New York Knicks 43
Milwaukee Bucks 43
Cleveland Cavaliers 41
Miami Heat 39
Indiana Pacers 38
Charlotte Hornets 38
Brooklyn Nets 36
Chicago Bulls 29
Atlanta Hawks 25

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