Decisive: if the decision was not made, there's a good chance that the other party would've won. SCOTUS must reasonably believe it to be likely decisive (as with Bush v Gore).  So that's likely to happen directly after the election, or something that e.g. makes Pennsylvania impossible to win for one party

Controversial: decided by me, in conversation with traders, based on a high level of controversy in the mainstream legal community.

Bush v Gore would be classified as 'Yes, in favor of Republicans', even though some recounts still had Bush winning. 

https://en.m.wikipedia.org/wiki/Bush_v._Gore