I've attached an aerial view of the Whittier site. Speed circle on left, stunt circle on right, and racing circle on bottom. I hope this will aid the discussion.
I've added a line 75 feet long that starts on the 15 foot radius circle in the stunt circle and heads toward the speed pits. It appears to me that a pilot standing on the 15-foot radius circle could hit a chair at the 91-foot mark with his outboard wing. --- Could the stunt pilot have mistakenly taken off from the 15 ft(racing/pitting circle) rather than the 5-ft radius stunt pilot's circle??
Please note how visible the markings are. Kudos to those responsible for maintaining the field.
The unregulated, public grass area to the right is only 86 feet from the center of the stunt circle, i.e. closer than the damaged chair.
Note: The dimensions above are based on scaling from the Google Earth aerial view and their "ruler" function. Accuracy = ? My guess 1 to 2 feet.
Randy