A "fist caddy" is a slang term for someone who enjoys fisting or cunt punching (see Cunt Puncher). The person who is the "fist caddy" is the submissive or receiving party who is being penetrated by someone's fist for pleasure. A "fist caddy" can be of any gender.
Aly hated to admit it, but she had officially become Kate's FIST CADDY! She was a total bottom who loved getting fisted! Who knew she could be topped!?
He was a good boyfriend; he knew how much Ivan loved to get plowed, face down, ass up, fisted almost all the way up his arm. Ivan was the best fist caddy he ever had. Ivan worshiped his powerful hands with both cheeks as if in prayer. Yes, Ivan was a keep for sure!