Bill's pdf shows something completely different. The pilot is holding
the stick too far back in the early stages of launch & the elevator is
pushing the tailwheel down on to the ground even after the
mainwheel has taken off. That's just poor technique & usually
happens because the pilot is behind the aircraft & blindly pulling
back after the glider starts moving.

A Discus is a "taildrager" which normally sits tailwheel-down.