The group of 6 airplanes were practicing formation flight for an airshow the following day. The airplanes were to takeoff in three groups of 2-airplane elements. The pilot in the lead airplane in the first group reported that, during taxi to the runway, he had come to a stop at the hold short line. The pilot who was in the second airplane, which was taxing behind the lead airplane, became distracted with the radios before looking up and seeing that the lead airplane had stopped. The pilot applied excessive braking; however, the tailwheel lifted off the ground. To prevent the propeller from ground impact, he released the brakes and the airplane collided with the lead airplane’s empennage. The lead airplane’s rudder and elevator were substantially damaged. The second airplane received minor damage. Neither pilot reported that there were any mechanical failures or malfunctions with either airplane that would have precluded normal operation.