Also, since the yaw control is achieved with different blade angle on the two rotor(which generate different torque), a combinations of left bank and right rudder input when flying with some speed will create forces that push the rotor tip toward each other on the right side of rotors and increase the chance they hit each other. And the faster you fly the closer this control in put will bring the rotor blades.
Try not to apply left bank and right rudder at the same time when flying fast :)