I noticed a lot of people at the dog park using these.  Truly great for keeping dog slobber off your hands.  Very easy to use. Hold onto the handle and pretend you are throwing overhand, but stop short and the ball sails out. Maybe obvious to you and I, but I have seen a few folks looking sheepish when they couldn't make it work right off - My dog loves to chase and retrieve, and this keeps my arm from getting sore.