This is the first game of the series where both teams will be playing with desperation. Boston doesn't want to go down 3-1, and Miami wants to put a stranglehold on the series. With arguably 2 of the top 3 defenses playing, you gotta bet the under in this situation.
Rondo will be playing hurt or be out altogether. Boston will be in the half court all game long. Boston showed in game 3 that they will also prevent Miami from fast breaking in this building. Could see this at 180 or below at tipoff.