This is very easy as long as you know what you are doing. Also your sensor bar has to be at the bottom of the T.V. screen.
First hold the wii remote waist level standing strait at the t.v. Make sure that the remote's sensor (the black thing on the top) is facing the sensor bar. Next just quickly flinch your hand down then up and the fast ball will be 90mph- 94mph. This does not work with curveballs, screwballs, and splitters, although you can try if you want.