To the best of my knowledge it is independent of their skill and only involves Wins, innings to earn them along with the defensive shots.
I would THINK win rate matters, but my own experience made me question that.
I had a high win rate for many sessions in a row, but didn't go up.
Then one day, after a long time, I finally did. I played at the new level for exactly one match, and lost that match.
The next week, I'd gone up again. Seems weird. Like win rate didn't matter.
We have a guy who's been a 6 for a while, I think he's a 7 or close enough, but he never goes up, and his win rate is 70+%. Can't figure it out.
This is the single biggest issue which is why low level players or players that do not know the game and/or pay attention shouldn't be keeping score. I had one match that went 39 innings between a 5 and a 6 in which the 6 swept the match. If I recall correctly, I had marked 36 defs with a vast majority on the 6. At the end of the night the captain, whom is a 5 and had less than 10 marked, came to sign the sheet and wasn't happy about that. I simply said every shoot that they did not attempt to make a ball is a defensive shot. The response was classic "He was just trying to get a good hit on most of those!". Which I pointed out was by definition is a defensive shot.
I get what you're saying. Safeties are definitely not marked carefully.
I actually agree with the other guy though, as far as kicks.
I honestly think most kickers don't intend to play a specific shot, but they also don't intend to play a specific safety. I guess the letter of the law says you mark a safe if they aren't playing a specific shot. But some shots are just hit and hope... neither a planned shot nor a planned safety.
In my mind, a defensive shot is planned where there's no chance of a ball going in, and it doesn't even occur to the shooter that a ball might go in. If they hit a ball and know they could slop something in, and part of them is hoping for that, it's not really a defensive shot.