How to get fastball pitches over 150 km/h in wii sports (baseball)?

The trick to ultra-fast pitches is a fast, but short movement, like flicking your wrist:

Quickly flick your wrist instead of throwing an actual pitch. This is the catch: quickly flicking your wrist will make the controller think you're making the "throw" motion a lot faster than you actually are.

Another tip compared it to trying to swat a fly - a sharp downward motion.

I've found the best method is to kinda throw a direct punch (as if boxing), which 95% of the time results in 150-153km/h fast balls.

You have to flick your wrist and depending on how fast you flick your wrist, it will normally result in 93/94 miles an hour.