Had this happen to me sort of.

I was flying and the stab flew off (screaming 2 stroke 5ft away, so couldn't hear the flutter), killed the throttle, and lost a signal(or something?). Plane heading towards the pits, and my mate flying off to the side. It was heading for him, so I yelled "Watch It" (again screaming 2 stroke 5ft away) , grabbed him by the back of his shirt, and pulled him back about a second before the thing plowed about 1 ft from where he was. Lost his 1/4 Cub, but that was all, we are both fine, bit shaken but fine now.

At the field now, if planes are in the air, during start-up each flyer is allowed 2 5-second full throttle bursts, so if someone does yell something EVERYONE knows.