A MA7 Instructor reported the aircraft nosed over during landing after the pilot tapped a brake when inputting rudder for a crosswind and because his student's hand had the throttle held rigid he was unable to add power to go around.

Narrative

The pilot approached for landing in a stabilized fashion. The pilot flared the aircraft close to the centerline of the runway. During the landing flare; the pilot allowed the plane to drift slightly off centerline and the plane's longitudinal axis to become misaligned with the plane's direction of travel resulting in a tail wheel 'shimmy' as the tail wheel contacted the runway. To alleviate the shimmy; the pilot attempted to ease backpressure on the yoke; but instead pushed the yoke slightly forward. Concurrently; the pilot attempted to align the plane's direction of travel with its longitudinal axis by adding rudder. While pushing left rudder; the pilot contacted and actuated the left brake. The plane's nose pulled hard to the left and its tail lost contact with the surface. As the nose lowered; the instructor pulled full-aft on the yoke; attempted to straighten forward direction with rudder; called for power; and attempted to add power in an effort to get the tail back on the surface. Full yoke backpressure did not correct the tail position because the plane's low airspeed rendered the elevator ineffectual especially with brakes continuing to be applied by the pilot. The Instructor was unable to add power because the pilot's hand was locked up on and covering the throttle. The pilot did not add power. As the plane continued to nose over; the Plot braced himself by adding more pressure to both brake pedals. The nose-over continued with the prop; spinner; and cowling impacting the runway. The Instructor secured the aircraft and advised CTAF of disabled aircraft on the runway. The Instructor; pilot; and airport personnel immediately removed the aircraft from the runway. Instructor observed no damage to anything except the aircraft.