and a key field which is a text field made up of Date & Venue & Game number.
This data should be recorded in 3 different fields, only one of which would be a text field. The other two would be a date for the date and a number for the game number.
It is only a flat file database at the moment.
FileMaker is a relational database system for a reason and if you don't take advantage of that capability, your ability to work effectively with this data will be severely limited, prone to error and very inefficient.
You describe data that really should be in at least three related tables, Games, Players, PlayerStats.
Players::__pkPlayerID = PlayerStats::_fkPlayerID
Games::__pkGameID = PlayerStats::_fkGameID
Your minimum figure can easily be calculated from a calculation field defined in the players table by using the count function to count the number of related records in PlayerStats.
For an explanation of the notation that I am using, see the first post of: Common Forum Relationship and Field Notations Explained