Question about fair catch

[JakeD17]

Please help me out with the following scenario:

R1 signals for a fair catch of a punt while the ball is in the air. The ball hits the ground several yards in front of R1 who then attempts to pick up the ball. K1 then creams him. What do you have?

My fellow officials say that R1 is still afforded protection and there should be a flag on K1. What is the difference between that and an onsides kick that has hit the ground? If R1 is standing at his free kick line and the kicking team attempts an onsides kick, can he signal for a fair catch if the kicker pops the ball up in the air by kicking the ball into the ground?

I would appreciate any answers you guys can give me. Thanks in advance.