I have to ask, were you changing the plug as a "service" job, or because there was an issue. You mention a splutter/misfire, did this start whilst riding and you limped home ?
Asking because to me it appears an issue with the plug, if the engine turns over, and there is no nasty grinding or noise, it could be that the plug part has exited out of the cylinder head.
With luck, get the rubber end out, undo the plug, put new plug in, start engine and away you go
without luck, spanners out. !!!