Term used by police in the UK. A "Hard Stop" is where a suspect is given no pre-warning (no shouting of "Police, stop!" etc) and where the element of surprise gives officers the advantage.
Hard Stops are most commonly used on suspected drug dealers (to prevent them disposing / swallowing the evidence) and suspected armed individuals, to prevent them from opening fire.
"Echo Zulu 714, urgent assistance - possible drug deal in progress on West Street, anyone to backup?"
"Control calling any patrol... 714 requiring assistance on West Street."
"Echo Zulu 21, we're responding - is this a hard stop?"
heart: I'm hard, veiny, and filled with blood. I throb and pulsate too. I usually stop throbbing, when I'm not inside of you. What am I? A heart of course!