back·stop 
(băkstŏp′)
(băkstŏp′)n.
1. Baseball
a. A screen or fence used to prevent the ball from being thrown or hit far behind or to the sides of home plate.
b. A catcher.
2. Something that supports or bolsters.
tr.v. back·stopped, back·stop·ping, back·stops
1. To serve as a backstop for.
2.
a. To support or bolster: "The firm lacks a topflight strategic-consulting arm to backstop its technology gurus" (Alex Beam).
b. To substitute for (another) in an emergency.