Interesting - could the sudden yaw before becoming airborne suggest a power failure ?
Probably just old fashioned propeller theory - An attitude change leads to changes in the directional forces from the propeller and even the forces (drag) on each wheel. Quite possibly a classic case here of the drift and slower acceleration due to attitude change. Then even more drag from the sloping grass surface possibly leading to a slightly longer than expected TORR.
The propeller theory related to this accident will most likely be quoted in tail dragger lessons for years to come.