Is this a shot just prior to impact? If so, it is very odd that the tailwheel is down (shouldn’t have been enough time) and that the pilot is not visible.
This has been speculated on repeatedly. It's likely due to excessive g-force, vibration, or both. The consensus is the tailwheel lock was broken in the pitch-up. As for the missing pilot, either he's hunched over the controls in the front or the seat broke and he's all the way back. The g-force in the pitch-up was extreme (9+), and probably caused a blackout. The force might even have broken the seat. The aircraft rolled into a inverted dive in what looks like a torque roll - rotating around engine torque from the ultrapowerful modified engine. That may not have been a controlled maneuver.
I am not a high-performance piston pilot, and I don't understand nor would I speculate about what actions a pilot might take to recover from this condition.