I suspect you will either need a custom method such as (Game *)insertGameForTeam:(Team *)team and do your team checks there or else handle the relationship conditions in - (void)willSave if you need to keep it at the model level.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.