It has to be one of:
-at least 7 fleets on each side
-at least 7 defending fleets and attackers lose < 15% of their ships
-at least 6 attacking fleets losing 90% of their value
-at least 4 attacking fleets and 10 fleets total where both lose > 70% of their value
more suggestions welcome (in that sort of format), it isn't too hard to add them in