Backstop

['bækstɒp] or ['bæk,stɑp]

(noun.) a precaution in case of an emergency; 'he acted as a backstop in case anything went wrong'.

(noun.) (baseball) a fence or screen (as behind home plate) to prevent the ball from traveling out of the playing field.

(verb.) act as a backstop.

卡斯特罗校對--From WordNet