The pilot was conducting a wheel landing to a full stop with a certified flight instructor (CFI) in the right front seat evaluating his performance. Upon touchdown, as the tail wheel started to come down, the airplane veered to the left. The CFI got on the controls with the rated pilot. Both pilots applied right rudder. The CFI stated that it felt like the right brake had locked. The airplane continued to the left. The left wheel went off the runway and the airplane nosed over. Examination of the left and right brake assembly revealed no anomalies.