One point of confusion that isn’t pre-determined by the rules is the difference between the lead and supporting actor categories. I saw somebody here on the SDMB (don’t remember who or where) claim that the order of listing in the credits somehow determined whether somebody was considered a lead or a supporting actor, which is bullshit. I was going to post a correction, but I didn’t get around to it.
The categories are governed by section six, paragraph four in the rules:
In other words, the rule does not define the difference between lead and supporting performances. That’s probably the biggest reason the actors in Lord of the Rings won’t get many (or any) nominations, because in an ensemble of that size, who are the leads? Aragorn is probably a lead, but when you’re competing with fifteen other major characters, how do you say that for sure? Isn’t everybody a supporting actor in that kind of ensemble?
That’s part of why the studios put out the “for your consideration” advertisements, in order to position an actor for a particular role. Consider Ethan Hawke in Training Day. Obviously, he’s the co-lead. But the studio didn’t want him competing with Denzel Washington, so in all the courtesy advertising they made sure to position his role as “supporting,” as little sense as that makes. And sure enough, they secured a nomination. Without the advertising, the role would no doubt have split the vote, and he goes nomination free.
I suspect that’s part of what happens with the Lord of the Rings crew; in the unlikely event any of them manages to get enough support, it’s going to be spread between the two types of categories, and won’t accumulate enough nominating votes in one type to qualify. The exception this year might be Sean Astin, who has a pretty good shot at a supporting nomination because the nature of his role — supporting Frodo in the quest — lends itself to that sort of interpretation.