RedactedNarrative: Chain O Lakes Water Ski Club was practicing show act of Boat O's or 360 degrees around boat, where boat turns sharply left, whipping a slalom skier to right, boat reduces speed and turns wheel back to right as slalom skier skis/swings around bow of boat, back to the stern as boat steadily increases speed to keep skier on plane, thus skier completes a full circle or 360 degrees around boat when skiing.  In this instance there were two skiers on separate ski ropes, one fell off balance at apex of ship, cart-wheeled in air and onto and into / impacted water, causing strain / injury to back.  victim was brought to shore and transported to Medical Center in Waupaca for his injuries, treated and released from ER.