No Fair Catch..

[linesman]

I saw this today and wondered how I would handle it as a back judge on Friday night. K punts. R1 who is in position to receive the scrimmage kick,
does not fair catch, and lets the ball go behind him. K2 who is charging full steam down the field "lights up" R1 with a legal hit. R1 was not in a position to protect himself.. There was no flag.. This was the NFL. I am not sure.. Would this wouldn't constitute "Illegal personal contact"?? or maybe it's just the nature of the game. If this type of thing would happen away from the ball it would definitely be a penalty. Opinions ?????