I've caught hundreds of minnows/mullets with a cast net...and now looking back....it seemed like quite the mystery to me too the first time I did it. A couple dozen throws, though...and I could do it right every time. It's really not that hard...you just need to adjust your thinking.
Most people treat it like a large frisbee...which is why it doesn't open up all the way...but closes back on itself.
Think about the motion your body would go through if you had to bend over to lift a heavy box off the ground and onto a truckbed without moving your feet...and the box is off to one side. It's a heave-ho operation. Not a spin move. No wrist flick. More of a forward fling.
Also, couple that with the 1/2-turn knife throw (or mumble-t-peg) concept...as in, your not trying to spin it open...but throw it out in front of you...with just barely enough spin to get it open.
You put one part of the net in your mouth to keep the net "reigned in" for a micro-second before letting go. Helps spread the net out completely.
Don't get any fantasies about throwing it yards out in front of you...at best, 5 or 6 feet.
Now, this technique applies to a large (7') net with weights used for saltwater.
I can't throw the small minnow nets...or, at least...I never needed to.
