great posts Fishmonk
I think we are all right in different ways - maybe that's another indicator of (his) genius
I think there's another basic component no-one's mentioned yet: your peers - if contemporaries who are themselves at the top of their game are in awe of you its another strong indicator that you are something very special
some fun indicators of genius:
1 - McCenroe - impossible slice
2 - Georgie Best - imposible dribble
3 - Brian Wilson - ultra-spook fade to Vega-tables - hey its art so has to be defined differently to sport