There's nothing worse in wrestling than a crowd that doesn't react to a match, and on the flip side, there's nothing better than a truly hot crowd. In the best-case scenario, arenas full of jaded fans who know all the backstage happenings still get truly invested in a bout, cheering for the man or woman they want to see emerge victorious.
One of the best displays of fans' preferences is the "Yay!"/"Boo!" spot, which typically comes late in a match and involves two wrestlers trading punches or other strikes. The popular wrestler will land a punch and the action will pause as the fans scream "Yay!" Then, his fatigued opponent will hit a shot of his own, giving them the chance to "Boo!" in unison. This is typically repeated a few times.
The quick bursts of noise make the match feel even more dramatic as it goes down the home stretch. Unfortunately for WWE, though, the "Yay!"/"Boo!" seems to be most pronounced when fans are supporting a heel and booing a babyface - namely, when Roman Reigns or John Cena are in main events. Still, it's a unique form of interactivity, even in the wholly-original medium of pro wrestling.