The current highest grade for Run and Gun is said to be an A+ but if you play on a save where you have already beat the game a perfect score is a S rank. This should be updated in the rules so we don't need to have a separate save just for Run and Gun runs. I'm submitting a run right now and don't think it's fair to me or anyone else that it gets disqualified because it's an S grade instead of an A+.
The rules are indeed worded a little poorly there (and the category name aswell I guess), we will get working on that.
Runs just need to achieve the Highest Grade, meaning having all the stats "completed" (golden time and all stats full). There are already A+ aswell as S grade runs on the boards, I do agree though that the rules need a little update in that regard.
Edit: Done, rules should be clearer now.
P is kind of an outliar, there's a seperate category for that aswell (as it has very different requirements than the usual grades).