I really love air shows, but there was an accident at the EAA AirVenture show in Oshkosh Wisconsin when I attended a few years ago. I understood one low-wing P51 landed atop another, since the wing prevented the upper pilot from seeing the plane below him. We saw the commotion, but I'm glad we didn't see the actual crash. The video looks a bit different from what I understood had happened.
https://www.youtube.com/watch?v=PLnKYJLzjjI

-Joe-