Ouch.

any ideas on how or why this happened

I would guess you have a broken valve and/or valve spring

Is your valve cover cracked? (Like maybe from a piece of the valve train hitting it on the inside)

Were there any metal bits in your oil? (Piston pieces from piston contact on broken valve)

As a start, you should pull your valve cover, to see if one of your valves has come apart and/or a valve spring is broken.

Oh, my gosh!
Probably no bearing on this one, but the last time I experienced a plug like that was in my Yamahammer after it burnt a hole in the top of the piston. (Was running lean)

I've done that a few times. Any chance that particular plug is platinum? If so, get it out of there. Never use plats on a supercharged engine. Copper or irridium only.

That plug could have done that for a dozen different reasons. So how about giving us more specifics on how old it is and what brand, model, and type it is?

hey i finally got the car fixed, i had a huge hole in my piston the one that had the bad plug. when it was all said and done the cost was a bit over $600 for parts and my dad did all the labor. runs great now. thanks for all the input and help offered.