My group is trying decide if we can or can not.
closed as unclear what you're asking by SevenSidedDie Nov 16 '17 at 4:20
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If you want, sure
The basic rule of D&D is on p. 6 of the PHB.
The DM describes the environment. - "Here is a guy with arms."
The players describe what they want to do. - "I want to rip his arms off!"
The DM narrates the results of the adventurers’ actions. - "You rip his arms off."
However, there is no mechanic in the rules that supports this
Combat in D&D is abstracted - "damage" occurs against a generic pool of hit points so there are no rules that cover targeting specific body parts or determining the effect of losing those parts.
If this is something you really want to do, there are RPGs that do deal with this. Or, you can come up with your own rules.