I just happened to read the NTSB report on that one a few minutes before hitting this thread. It was the pilot's first solo in the P-51, which was a two seater. The instructor had landed with him, got out and told the tower it would be an initial solo. The pilot made a circuit, touched down and started a touch-and-go takeoff when it went on its back.
It's interesting to note that the final production P-51H was built with a much taller fin and rudder in an attempt to provide a better means of handling the torque roll problem.
Several of the earlier models have been retrofitted to include the larger tail as well.
I knew the pilot and the instructor and my heart breaks for both. The instructor is an amazing guy with a spectacular resume.
He would be the first guy I’d call if the lottery fairy drops a P-51 in my lap.