The Heat's defense reminds me of Rex Ryan's front seven from his Ravens days. His scheme relied on heavy blitzing and versatile players flying to the ball and confusing offenses. The Heat's defense is very much based on having mobile players who can defend multiple positions, and stressing the ball-handler before the offense can get established. Both defenses are susceptible to smart passing and anticipation. The Heat, like the old Ravens, have the speed to recover a lot of the time, but over the course of a game, they'll get tired from all the running. Parker pushing the pace and moving the ball constantly should help get the Heat gassed.
Also of note, the Spurs have defenders who can guard all three of the Heat's best players in their starting lineup, whereas the Heat have no one to guard Parker or Duncan. If Parker plays his game, Chalmers can't stay with him, and Bosh/Haslem should be Duncan's weakest primary defender this whole post-season. Green, Leonard and Splitter shouldn't be expected to stop the Heat's Big Three, but they are at least defense-first players with the size and quickness (and recent experience) to make them work. All three of them need to play well enough on offense to be defended. Green either keeping Wade honest or abusing Chalmers is necessary, and Leonard should get his opportunities to hit threes and drive on smaller defenders. If Battier is on him, he needs to at least be as effective as he was against Prince.
Splitter, as I've said before, is the key to this series. He needs to win the match-up with Battier, like West has. Doing so forces Spoelstra to play big, which hurts the Heat's spacing on offense and mobility/flexibility on defense. With the bench, he needs to keep Anderson busy, to prevent him from free-lancing. Splitter also needs to be a beast in the PnR to force Miami to move.

