Not in the formula, but you can use the filter to filter out all of the tournaments other than the first 10. You can create a season to do this and assign the first 10 tournaments to that season, or more easily you can just set the start and end dates of the filter appropriately to grab only the first 10 tournaments.
Let me clarify...
Person A plays in Games 1,2,3,4,5,6,7,8,9,10,11,15
What you suggest above would work.
Person B plays in Games 1,3,4,5,8,9,10,11,12,19,20
Their first 10 games do not happen to coincide with the first 10 games of the season.
Hope that sheds some light onto my quandary.