fair catch is, in effect, a trade. The receiver gives up his right to advance in exchange for freedom from contact by the opponent. One potential catch (pardon the pun) to the deal may be a muff on the part of the receiver.
In PlayPic A, the receiver has given a valid fair catch signal, then muffs the ball (PlayPic B). If the covering official rules the receiver could still make a catch, the action by the team K player is kick-catching interference in NCAA. The receiver may not be contacted until it is no longer possible for a catch to be made (6-5-1b).
Such is not the case in NFHS. The receiver’s fair-catch interference protection ends when he muffs the kick (6-5-6, 6.5.6E)