That's asking for ping and detonation and bad stuff. Looks like something got in there and rattled around for a bit. Take a good hard look at that plug, see if some ceramic came off the center electrode. Maybe a light application of emery paper would help smooth those scars out. Use a shop vac while doing this, and go lightly. What's the bore look like?
Might be running just a tad rich. You also wanna take a good look in the ports on that cyl, make sure there's no damage there either. Prolly wanna compress the valve springs so you can take a peek at the seats as well.