The motor doesn't have to disengage; when unpowered it turns into a freewheel. The onewheel is perfectly capable of coasting, that's not what causes the crash.

The motor doesn't have to disengage; when unpowered it turns into a freewheel. The onewheel is perfectly capable of coasting, that's not what causes the crash. It's the stance of the rider (leaning forward) combined with the sudden lack of acceleration from the motor which disrupts the equilibrium of forces and causes the ensemble to tip forward -- then it all comes to an abrupt stop because the leading edge digs into the ground.