back·stop / ˈbakˌstäp/ • n. a person or thing placed at the rear of or behind something as a barrier, support, or reinforcement: bullets volleyed into the backstop of a flood-control canal. ∎ Baseball a high fence or similar structure behind the home plate area. ∎ inf. Baseball a catcher: he tore the chest protector completely off the big Yankee backstop. ∎ fig. an emergency precaution or last resort: the human operator has to act as the ultimate backstop when things go badly wrong.