Nick Cannon stopped by the Knicks game on April 2 to film a promo for America's Got Talent, that show where all the contestants sing except for one person who juggles dogs, or whatever. The Madison Square Garden crowd did not appreciate Cannon's presence.
While Cannon went through the motions of the spot—hey, he's not really sinking that no-look basketball trick shot!—the crowd mercilessly booed him. The jeers went on for a good three minutes before Cannon finished his duties and peaced out.
They can probably edit most of that in post.