I'm looking for the German phrase most likely to be used in a tense, dangerous situation (in which a sudden move could get one shot) to warn people to stay put.
To be more precise, the warning is coming from one of the good guys, yelling to the other good guys not to move.
My author has "Ort und Stelle bleiben!", but I fear it was arrived at by direct translation, and is unidiomatic.
An Ort und Stelle has the doubled "place" to assure someone or something is reliably there. That's not what you intend to say.
Sei an Ort und Stelle!
Be at that place reliably!
Bleib an Ort und Stelle!
Stay at that place reliably (I need you to be there)!
Better phrases for your situation just use the verb bleiben:
Bleib, wo du bist!
Bleibt, wo ihr seid!
Telling someone to stay put.
Bleib weg!
Typical warning from someone at a dangerous place or from someone attempting suicide.
Bleib stehen!
Telling someone to stop walking or running.
Stehenbleiben!
Typical movie cop yelling at the bad guy.
Sometimes other verbs match better:
Nicht bewegen!
Typical bomb defusing phrase.
Halt still!
Typical phrase of someone cutting someone else's shackles.
If time is as much an issue as you described I would recommend "Halt!" as a quick shout.
