The key to this decision is whether the ball was in play at the time of the stomp, or had it already gone for a goal kick. Remember, you can only give a free kick (direct or indirect) if the ball is in play.
Irrespective of whether the ball was in play or not, the defender should be sent from the field for violent conduct. Now to the restart. It will either be a goal kick or a direct free kick (where the stomp occurred) dependent of if the ball was out or in play at the time.
1)The nature of the foul, being careless, reckless or excessive force. Stomping is more likely to fall in the latter categories in particular excessive force. This of course will determine if the referee sends the player off, cautions him or applies no sanction (unlikely to occur in the above situation in particular).
2) Was the ball in or out play? This will affect the restart of play.
OK, what I was thinking was that in the Violent Conduct discussion in the LOTG, the duty of the referee is that they MUST move in quickly to actively intervene in the situation, and try to avoid any mass confrontation.
"Referees are reminded that violent conduct often leads to mass confrontation, therefore they must try to avert this with active intervention."
That is an interesting point, the referee should not sit back.
I suppose that is not to say go and get in the middle either. But if you quickly get over to the incident area, you are likely to assist help the situation rather than it get out of control.