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The Celtics are crushing opponents in the third quarter

Boston’s lockdown defense coming out of the half puts them in rare company.

Philadelphia 76ers v Boston Celtics

This season we’ve seen a familiar trend in Celtics games. Hang around in the first half (or fall behind by 15 depending on the night). Then play lockdown defense and let Kyrie cook in crunch time. While it can be a little frustrating, Boston’s record speaks for itself. One big factor in Boston’s wins this season has been dominant third quarters. The numbers highlight how incredible the Celtics have been in that period this season.

Boston outscoring their opponents by 16 points per 100 possessions better. Their net rating is second only the Warriors, and comfortable ahead of the Rockets. The breakdown is interesting too.

3rd Quarter Efficiency

GSW 123.5 96.4
BOS 110 94
HOU 110.8 98
DEN 112.9 102.2
MIL 109.2 102.6

The Warriors are in a class of their own, as their offense rating jets up to an absurd 123 points per hundred possessions. They bury teams with threes, while also playing elite defense.

But the Celtics are an interesting contrast to the rest of the list. Their offense improves a bit, but the defense goes to another level. Boston’s third quarter defensive rating is awesome. They allow only 94 points per 100 possessions, by far the stingiest third quarter figure since the 2013-14 Pacers.

Looking at Boston’s most played 3rd quarter lineups can help show who is driving this trend.

3rd Quarter Lineups

Starters 56 10
Morris for Baynes 43 -17.4
Smart for Baynes 24 43.2
Smart for Kyrie 15 54.7
Smart for Tatum 13 81.1
Smart for Brown 12 43.3

The starting lineup performs well. Then the Morris lineup gets caved in. But the addition of Marcus Smart sends them into the stratosphere. Each one of the most played lineups with Smart performs extremely well. Smart’s individual net rating in the third quarter is 28.1, the highest (non-GSW) number in the league. This season, the team has been at its best with Smart on the floor, and its no exception here either. Also worth noting that Smart overlaps with Al Horford a lot as well. Sharing minutes with a perpetually underrated all-star certainly helps his numbers.

There are small sample quirks in there to keep an eye on. The starters play at a glacial pace and rebound 94% of opponent missed shots, the latter of which can’t be sustainable over a full season. The most played lineups with Smart are only allowing 15% from deep. (I’m a three-point defense truther, but even I have my limits). The numbers can get skewed by one especially nice stretch, etc.

So there’s a little luck, but it can’t just be that. Half-time offers the chance for coaches to make adjustments. It’s no secret that Stevens is one of the best coaches in the NBA. So naturally he and his staff will use halftime adjustments to tweak strategies during games.

You won’t see the Celtics running the Triangle or playing zone for a quarter. But they aren’t afraid to hedge a little more on pick-and-rolls or target specific mismatches for example. At the very least it gives them time to figure out what’s working and what needs to be switched up.

Stevens is quick to temper expectations about the extent of their changes. After the recent game against the Pistons, Stevens said

“I’ve always thought that the whole halt-time adjustments thing was a little overrated... We usually make one to two small tweaks, but nothing major.”

This is the first season under Stevens that the Celtics have had such a pronounced improvement in the third quarter, so that quote may not just be humility speaking. The last few games have chipped away at the insane margin a bit too. Regardless, it’s still a trend worth thinking about, especially as Stevens continues to experiment with the rotations.

Whether it’s Stevens’s wizardry, Smart’s inexplicable knack for improving the team, or just good old-fashioned luck, the Boston Celtics have announced themselves as a team to fear after half-time.