Our defense is not the typical physical, hard-fouling, lots of steals and blocks type defense.
Its a modern-day defense. You can't be that physical anymore. You have to disrupt rhythm. The Celtics disrupt the rhythm of the main ways the other team wants to score. It is designed to force ball-handlers into mid-ranger shots, take guarded threes, or attempt to score one-on-one. Those are things modern NBA offenses do not want to do.
This kind of defense requires disciplined position from every player, high IQ from every player, high versatility from every player, and a high feel for teammate position from every player. The Celtics have that in every player on their roster.
Teams can't pick on weak spots. They can't get the shots they want. They can't get into rhythm.
This is no small sample size. They were this good last season too. They were this good in the playoffs. They will just get better as Tatum and Brown get better and Hayward gets healthy.