I am a new volleyball coordinator. I cannot wrap my brain around how to calculate this simple math problem.

The question a coach brought up was, Since coed games don't count, should the ranking be based upon percentage of available sets won against girls only?Some teams had less sets/ matches possible than others.

The answer I received from the city was, To answer the question below, the person is correct in that win percentage would be calculated regarding games played against girls teams. Cross over games will continue to not count in the standings and will not be recorded in the win and loss total. All games reflected online in the standings will be accurate and win percentage will be taken from the win loss. The person is correct in that some teams will have more games counted than others but this will not affect the overall standing.

My question is how do I figure this out? I know it is going to be stupid simple; it is just not clicking for me today.