Despite glitzy rating, Celtics defense isn't getting stops when they need it most

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The Celtics have spent much of the 2018-19 season perched atop the NBA in defensive rating, allowing a mere 102.8 points per 100 possessions. And yet the eye test has made it hard to trust those numbers, so much so that even head coach Brad Stevens has been leery of Boston’s position.

“Our defensive numbers are great. I don’t think our defense looks great, but I guess it is,” Stevens said earlier this month. "At least that’s what people tell me.”

So, how exactly is one of the NBA’s best defensive teams starting at a middling 10-10 record? Simply put, Boston’s rating is a bit misleading and a team that has shown solid defensive play early in most games has turned into a pumpkin when they’ve truly needed stops.

The Celtics own a defensive rating of 95.1 during the first quarter of games this season, easily the best mark in the league, and yet that number leaps to 106.4 in the fourth quarter, which ranks 11th among all teams. Boston owns a defensive rating of 100.4 in the first halves of games (second only to Oklahoma City) but that number vaults to 105.3 in the second halves (though that’s still the eighth best mark in the NBA).

This might be the smoking gun: Boston’s defensive rating in clutch time — the final 5 minutes of games with the score within 5 points — explodes to 116.8. That ranks 22nd overall in the NBA and has contributed to the Celtics owning a meager 6-8 mark in the league-high 14 crunch-time games this season.

What’s surprising is that Boston’s typically anemic offense has been fantastic in crunch time, owning an offensive rating of 124.3, which ranks fourth in the NBA. But that Boston owns a positive net rating in crunch time and is still unable to routinely win those games speaks volumes about their defensive woes.

Opponents are shooting 46.7 percent against Boston in the fourth quarter of games, the sixth-highest percentage among all teams. Normally, we’d caution against putting too much stock in blanket fourth-quarter stats because lopsided games tend to skew numbers with trash-time play. But the Celtics have so frequently played in close games this season that it’s hard not to take the data at face value.

The other big issue for Boston: Opposing scorers have continually had big nights against Boston. It was one thing when it was Kemba Walker or Jamal Murray, it’s quite another when it’s Trey Burke and Jose Juan Barea.

The Celtics have been gouged, particularly in pick-and-roll situations. With that in mind, here’s a look at Synergy Sports defensive data with points allowed per play by Celtics defenders against pick-and-roll ball-handlers, last season compared to this year:

Player                   PPP 2017-18 (Percentile)  PPP 2018-19
Terry Rozier          0.773 (70th)                         0.846 (52nd)
Jaylen Brown         0.752 (76th)                          0.800 (61st)
Marcus Smart        0.845 (49th)                         1.109 (9th)
Kyrie Irving             0.822 (56th)                        0.810 (58th)
Jayson Tatum         0.613 (94th)                        0.789 (64th)
Gordon Hayward   n/a                                       0.743 (76th)
Marcus Morris        0.509 (97th)                       0.600 (93rd)
Semi Ojeleye           0.750 (78th)                        0.700 (84th)
Team overall            0.777 (2nd in NBA)          0.851 (15th in NBA)

Boston’s clearly slipped as hammered home by the overall team number. Smart’s numbers seem impossibly poor and he certainly had some tough nights, particularly against Walker. But before you rush to pin the blame on Smart for Boston’s defensive woes, he’s been fantastic otherwise. In fact, he’s been Boston’s best defender overall, based on points allowed per play, according to Synergy data. 

Smart has mugged opposing players in spot-up situations, limiting opponents to 18.9 percent shooting (10 of 53) and 0.492 points per play, via Synergy data. That’s impossibly good when you consider that, among players with at least 50 spot-up possessions defended, the next closest defender is Giannis Antetokounmpo at 0.707 points allowed per play.

So while Smart needs to be better in pick-and-roll, that’s a message across the board. Where has regression occurred in Boston’s overall defensive play from last season? 

Let’s look at point-per-play numbers for the Celtics overall this season and last: 

Player                PPP 2017-18 (Percentile)    PPP 2018-19
Horford               0.799 (91st)                             0.931 (47th)
Brown                  0.887 (63rd)                            0.878 (64th)
Tatum                  0.832 (86th)                            0.920 (50th)
Smart                   0.854 (78th)                            0.773 (89th)
Irving                    0.920 (48th)                            0.948 (40th)
Morris                  0.928 (43rd)                            0.864 (68th)
Rozier                   0.878 (67th)                            0.857 (70th)
Hayward                n/a                                         0.837 (75th)
Baynes                 0.739 (95th)                            0.886 (61st)
Theis                     0.850 (80th)                           0.865 (68th)
Ojeleye                 0.920 (48th)                           0.825 (79th)

The dips by both Horford and Tatum are most notable and speak to some of the issues Boston’s back line is facing. Horford’s blocks are up but he seems a step slow at times, and it’s fair to wonder if the sore knee that kept him out in Atlanta could be hindering him a bit. Like any young defender, Tatum needs more focus when he’s on the court, but has the necessarily physical tools to make things difficult when he’s in the right spots.

Ultimately, Boston has fallen victim to miscommunications and poor technique, and all too often in critical fourth-quarter situations. It reverts back to the notion that this team has to find more consistency and play to the level it's capable of for closer to 48 minutes.

As Smart referenced after Saturday’s loss in Dallas, the Celtics are not imposing their will on opposing players and letting scorers get too comfortable and confident. The Celtics have routinely made things tough for opponents and need to rebuild that personality.

If the Celtics’ offense was more consistent, maybe these defensive lapses wouldn’t be such an issue. But Boston continues to scuttle offensively and that’s put an even bigger burden on the defense.

Bottom line is the Celtics need more consistency on both sides of the ball but they can’t continue to allow late-game lapses to diminish the strong defense they’re playing for much of the rest of the night.

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