how on earth do u "parry" on pc

[Flatrateliner]

ive played through the game like 5 times now and i still dont know how to consistantly do the parry move in fist fights, yknow where you block and then attack in the same move.
It happens every now and then randomly but whenever i try to do it on my own it never works.
I only know that its suppost to work by pressing f while the attacker swings or something but no matter how i time it arthur just throws a punch or doesnt do anything.

[Mr.Ullrich]

Isn't it the "R" button?

Edit:
F punch
E grapple
R block

[Mozart]

For me, i press R + S (to walk backwards). If i do on the right time, i got the parry animation