According to DP Sullivan (Old Stones Of The Cotswolds & Forest Of Dean – 1999 Reardon), this is another of those hangman’s stones that takes its name from an idiotic thief:
It obtained its name, apparently, from an incident involving a sheep rustler who, when getting over the stile with his spoils fell and was hung by the entangled sheep. ... It is possible that this stone once marked a gibbet, giving a more plausible reason for its name.