The Australian Surf Lifesaving movement used to rescue people by donning a belt attached to a line. The beltman would swim out to the person they were rescuing while the team on the beach would feed the Line out as they swam.
The Belt had a Pin at the front that could be pulled to quickly release the Belt from the Beltman. If the Beltman was in difficulties they'd 'pull the pin' to get free.
It's a common term used by Australian Surf Life Savers to describe a decision to get out of a bad situation.