I think what you are doing with R2 is an Guard Counter ,you shield yourself with L1 and upon impact from the enemie you press R2 .
More Powerful ,consumes way more of the enemies stamina and higher poise damage.
Weapon arts in ER youse L2 for instance ,but you should wear a shield that has "No skill" so you can youse your main weapons skill .
Such as this one as example.
Read you played Ds3 as well,Ds3 as example doesn‘t have Guard Counters.
Hope it helps.