There are a number of Flash games called "Balance," so we'll call this one "Balance Involving a Racquet and Balls From Many Sports." You use the mouse to balance a racquet on end, while avoiding a bunch of falling footballs, soccer balls, and suchforth. Tennis balls, however, serve as power ups, making your racquet stable or blowing up all the balls. Simple, but fun.
Balance [Miniclip Games]