Hail Mary
Etymology
In American football, a "Hail Mary" is a long, hopeful forward pass thrown as time runs out. Quarterback Roger Staubach popularized the term after a 1975 game, saying he closed his eyes and recited a Hail Mary — the Catholic prayer — as he threw. It now names any desperate final effort against long odds.
noun phrase · /HAYL MAIR-ee/
A desperate, low-odds attempt made when nothing ordinary can still work.
What it names
The last-ditch gamble — the throw you make only because you have nothing left to lose.
Example
Cutting prices in half was a hail-mary to save the store before the lease ran out.
Related idea
A hail mary is a desperate long shot with nothing left to lose, whereas a gambit is a calculated sacrifice made from a position of strength.