Backstop and Stronghold

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

Stronghold and backstop are semantically related. In some cases you can use "Stronghold" instead a noun "Backstop".

Stronghold noun - A structure or place from which one can resist attack.

Backstop and stronghold are semantically related. Sometimes you can replace term "Backstop" with "Stronghold", this nouns are similar.