lol. Momma used to hassle me about grammar. When you are describing a condition contrary to fact, you use the subjunctive. I know you know, I'm just sayin'. The reason for it, in case any readers care, is that if you say "If O'Connor was on the court," it leaves open the possibility that she may have been, but you're not sure. By using the subjunctive, it makes clear that she was not on the court; you are merely discussing a hypothetical what-if.
Other languages (like Greek) are more explicit because there are different forms of the verb that distinguish between counterfactuals, probabilities, and improbabilities.