I found this idea on www.bettycrocker.com
Baseballs: Frost cupcakes with vanilla frosting. With black, red or blue icing, pipe 2 arches on opposite sides of cupcakes, curving lines slightly toward center. Pipe small lines from each arch to resemble stitches on a baseball.
Basketballs: Color frosting with yellow and red food colors to make orange; frost cupcakes. With black icing, pipe line across center of cupcake. On either side, pipe an arch that curves slightly toward center line.
Soccer Balls: Frost cupcakes with vanilla frosting. With black icing, pipe a pentagon shape in the center of cupcake, piping a few rows of icing into center of pentagon. Pipe lines from pentagon to edge of cupcake to resemble seams. With toothpick or spatula, spread black icing in center of pentagon to fill in the entire shape.
Tennis Balls: Color frosting with yellow and green food colors to make tennis-ball yellow; frost cupcakes. With white icing, pipe curved design to resemble tennis balls.