The Celtics have already faced two excellent defensive teams in the Atlanta Hawks and the Philadelphia 76ers. That isn't a cop out, the Celtics also are a team that struggles with their offense. None of that, obviously, makes the Celtics all that happy to have to face a team in the Miami Heat that are also known for their defense. In fact, they were second only to the Celtics in points allowed this year. (Rounding out the top 5 were the Bulls, Hawks, and Sixers - methinks this playoffs run was destined to be difficult from the start)
Still, the Heat do have some noticeable chinks in the armor that the Celtics could (when properly focused on the task at hand) in theory exploit. Let's let someone smarter than me explain.
The Pacers just weren't crisp enough to figure out Miami's aggressive defense. It's a defense that leaves gaps as Miami players trap and scoot around the court, but the Heat close those gaps more quickly than any other team. To beat Miami, an opponent has to make quick and accurate reads, throw precise passes and make a fair number shots. Waiting a beat can be fatal, and Indiana was caught too often waiting that extra beat.
In other words, no pounding the ball into the hardwood till 5 seconds are left on the shot clock - looking at you Random Rondo. No lazy picks, no half-hearted cuts, no broken plays and pray for teardrop buckets. The offense has to execute, execute, execute.
Ball movement is critical to breaking down this defense. If there's one pass and a contested jumper, that's not good. If the ball touches 3 or more hands, that's probably pretty good - so long as the passes are crisp and not telegraphed (which could lead to many highlight dunks).
Oh yeah, and it sure would help if the Celtics simply made open jumpshots when they have the opportunity - something that happened about as often as a blue moon against the Sixers and Hawks.
It should go without saying that the Heat are a formidable opponent. A good deal of attention will rightfully be put on the Celtics trying to limit James and Wade (and Bosh if he's available). But to overlook the Heat's defense is a mistake.
The Celtics are the savvy vets who know when and where to be and kill you with execution. The Heat are hyper-athletic youngsters that make up for their lack of fundamentals with blazing speed and hops. The Celtics simple need to execute their offense to take advantage before the Heat can recover. Sounds simple in theory.