Legcuffs are physical restraints used on the ankles of a person to allow walking only with a restricted reach and to prevent running and effective physical resistance.
Frequently used alternative terms are leg cuffs, (leg/ankle) shackles, footcuffs, fetters or leg irons. The term “fetter” shares a root with the word “foot”.
With respect to humans, shackles are typically used on prisoners and slaves. Leg shackles also are used for chain gangs to keep them together.
Chain Gang Street Sweepers, 1909
Metaphorically, a fetter may be anything that restricts or restrains in any way, hence the word “unfettered”.