Why bag R's touching? K is the only team that can "first touch".

You probably want to bag it for the fumble/muff.

If it is a fumble, yes. But a muff? What is the relevance of the spot of a muffed kick by R?

This pops up in numerous threads - bagging random spots.

Think about the purpose of the bag. It's to mark what could potentially be an enforcement spot for a penalty. Bagging a muff (or dropped snap) is improper mechanics. I've heard the argument that bagging a muff or dropped snap is done to show everyone else that you see a loose ball. Again - this is not proper mechanics (in NCAA, Fed, or NFL). Bag potential enforcement spots (or, possibly, other spots you may need... I've seen bags used properly to mark an out of bounds spot if the official needed to leave the spot for some reason (penalty cleanup, officials conference, etc), or to mark the spot that certain players leave the field.)

It should NOT be used to mark a spot that will not be needed.

You bring up a great point that is well taken. When I wrote my response, I was thinking fumble. I agree the muff doesn't get the bag. I added the /muff because I was thinking wrong. (I plead umpire ignorance your honor. I am never around when a scrimmage kick is fielded. My crew does drop a bean bag when a free kick hits the ground to be sure it met the went ten yards and touched the ground requirement. Clearly the muff on a scrimmage kick is different.)