[back.stop] n (1851) 1: something at the back serving as a stop: as a: a screen or fence for keeping a ball from leaving the field of play b: a stop (as a pawl) that prevents a backward movement (as of a wheel)
2: a player (as the catcher) positioned behind the batter
[2]backstop vt (1941) 1: support, bolster
2: to serve as a backstop to