What happened
During preparations for a launch, a runway assistant was occupied assisting with the launch of another glider. The pilot of glider N65843 chose to connect the tow line to his own aircraft. After the tow plane taxied into position, the glider pilot connected the line and entered the cockpit, seated in the aft position, while a passenger occupied the front seat.
The pilot then exited the cockpit to adjust his seat cushion. During this process, the tow pilot observed movement of the rudder and interpreted this as the signal to begin the launch. The tow pilot looked away and commenced the takeoff with only the passenger remaining in the glider. During the sequence, the glider was released, subsequently lost control, stalled, and crashed.