In advance, using royal icing, pipe 19 tip 6 ball heads on waxed paper. Pipe tip 1 dot facial features and pull-out hair. Let dry.
Ice half ball cake smooth with spatula. Lightly press paper towels on cake to achieve texture of basketball. Set aside.
Ice sides and 8 1/2 in. from top of 1-layer sheet cake smooth in white with spatula. Comb sides of cake with decorating comb. Ice the rest of cake top smooth in violet; sprinkle immediately with Rainbow Nonpareils.
Position basketball cake on foil-wrapped board. Pipe tip 4 black outlines on ball. Pipe tip 1A rim and tip 6 string basketball net. Outline backboard with tip 48. Cut out triangle pennants from colored paper, write messages and attach to toothpicks with icing. Insert pennants in cake. Pipe tip 32 shell bottom border. Position fans.