Actually, looking just now at my PDF of Arms Law Classic, it's 41-50 on the 2H Weapon fumble chart:Rolemaster 1980.
Man those crit and fumble chart....00 slip on an invisible turtle and decapitate yourself.
Stumble over an unseen imaginary deceased turtle. You lose 2 rnds of offensive action but can parry.
I'll check my physical copy of Arms Law later on, just to check that Classic didn't sneak in any changes!