This photo was sent to the S&S Tech Department. It shows the top ring land starting to bend upward below the valve pocket. Notice the gap above the top ring. In this case the thin land between the top and second ring also shows some damage. The beginning of the end!
The ring land is thinnest just below the valve pocket. Being thin, this area is the weakest, gets the hottest, and tends to break off when detonation occurs, as shown here. The rider obviously shut it down quickly, since there is only minimal damage where the piston hammered the fragments against the top of the combustion chamber.