One of the elements of Miami’s Game 4 win was the defense Dwyane Wade  played on Rajon Rondo  late in the game. Actually defense isn’t the right word. Wade was assigned the task of guarding Rondo, but he gave him such a wide berth that he was able to roam the passing lanes and help on anyone who wanted to take it to the basket.
This has been done numerous times before, of course, most notably by Kobe Bryant  in the 2008 Finals.
In truth, the Celtics  expected to see Wade guarding Rondo much earlier in the series. Doc Rivers  hinted before the playoffs even began that he figured that’s the way Miami would go. Now that the Heat are down to their last chance, the Celtics figure that they will see a lot of it in Game 5.
“We thought we’d see it much earlier,” Rivers said before the game. “They’ve used it in the fourth quarter and they’ve done it in special situations [end of the game, shot clock, out of bounds plays, etc]. Wade is really destructive when he’s guarding Rondo. He’s like a free safety. A very good safety.”
The reason Miami doesn’t go this route on every possession is that they need Wade to carry the load on the offensive end, as well. Although it should be noted that trying to follow Ray Allen  around all those picks is not a lot of fun either.
Rondo was asked after Game 2 if he was surprised that he hadn’t seen Wade on him more and he just shrugged. “They’re having maybe four guys guard me,” he said at the time. “Dorrell Wright, [Carlos] Arroyo , [Mario] Chalmers , Wade. I don’t really care who guards me.”
Rondo destroyed Arroyo in Game 4, and Chalmers hasn’t fared much better. Wade would be Miami’s best option, but can the Heat really ask him to be the best player on both ends of the floor? If they do, Rivers wants Rondo and Kendrick Perkins  to cut to the basket at every opportunity. They key, Rivers said, is for Rondo to stay aggressive, even if he doesn’t have the ball in his hands.