If the portal is unfiltered, GetNthRecord can be used to access data in the Nth related record.
RelatedTableField + GetNthRecord ( RelatedTable::field ; 2 ) + GetNthRecord ( RelatedTable::field ; 3 ) ....
I did filter the portal . I filtered for NBA season, minor league, and college. Is it still possible if it is filtered?
The filtering produces issues as calculations such as these will ignore any filtering action. But the filtering you describe sounds like filtering that can be done with match fields instead of a portal filter expression and that would then allow the original calculation to work.
Do you need to use these totals in further calculations or do you just need to show the total?
Are you using FileMaker 12 or newer?