I was watching some of the highlights of the game last night and thought I'd point something out. https://www.youtube.com/watch?v=ueZzruU0yLM
At the 1:00 mark, the Celtics run a common set. Hayward comes off a flex down screen on the left side. Rozier passes it to him and immediately cuts to the basket off a back screen by Williams. This creates confusion about who is guarding Williams, who then immediately sets a screen on ball for Hayward. At that point, Rozier is in the lane and sets a backscreen for Williams who is rolling to the hoop. This play has worked several times this year to open up lob dunks for Williams, Theis, and Horford.
What I found fascinating about this play in particular is the way the threat of Williams' lob dunk collapsed the defense. Admittedly, this was against a horrible defensive lineup (Joseph, Evans, O'Quinn, McDermott, Leaf), but all four help guys (Evans was one pass away on Brown) naturally drifted into the lane to clog up the alley-oop attempt.
This enabled Rozier to pop back out to three point line for a three that he made and got fouled on.
The threat of Williams' lob dunks is compromising the integrity of defenses -- backup defenses right now, but still defenses.
If this team keeps moving the ball like they are, and they force defenses to expand and contract back and forth multiple times on possessions, the Cs will be really difficult to stop.