Symbolism, Imagery, Allegory
Willie and Tom are both associated with the roar of the crowd. Willie brings the roar with his speech (and the action behind it). Tom brings the roar by making the right plays on the football field. Football and politics and the roar of the crowd. Nothing says American dream quite like either one. In contrast to the chorus of old men, the roar of the crowd represents the positive judgments of the community (though the crowd can switch from boos to roars very quickly).
The football thing isn't hard to figure out. Tom plays well and he gets the roar.
Willie's roar is more complicated. What a crowd will roar for says a lot about the crowd. Did you find anything odd about Willie's speeches? Here's an example of an excerpt from a typical Willie Stark speech: "'I have seen blood on the moon! […] Buckets of blood, and boy I know whose blood it will be. […] Gimme that meat ax!'" (3.92). As Jack tells us, "It was always that way, or like it" (3.93). When Willie is mild-mannered and calm, nobody listens to him. To get the roar, he has to constantly evoke violence. Willie's crowd is angry and confused. He succeeds with them by representing himself as "one of them," and by giving voice to their anger at having been cheated by the fat cats who get rich while others go hungry.