last stand

Short definition from Wiktionary

Noun

1. 1
   A military encounter, especially against (often greatly) superior odds, generally as a last resort, whether to save another army or city, or as a last act of defiance, and often resulting in the total annihilation of the weaker force. In general, it can also the name of the location of this clash. (In some cases it may become part of the local name.)