This was one of those spur-of-the-moment games a group of friends and I invented several years ago during church camp. It can be used for any game that uses a ball (softball, basketball, etc.), but volleyball seems to work best.
Essentially, the rules of the game apply; but the ball is lathered with shaving cream before use. In the case of volleyball, before each serve the ball should be lathered afresh—makes for some interesting play and an interesting twist, especially on a warm day. (You should be able to find some inexpensive cans of shaving cream for this, or make your own lather from dish washing detergent and a bucket of water.)
Other fun games to play with a lathered ball include kickball and touch football.
For another twist of fate, try playing ultimate lather Frisbee®. Bring your goggles.