The kanji here means past, but this verb means to leave. Think of it this way: when you leave, you put somewhere or something behind you, in the past.

This uses a new reading for 去, so here's a mnemonic to help you out:

You'll want to leave if you see a saw (さ) pointing at you. Saws can be deadly weapons, so you should leave immediately if someone is brandishing one at you. You just saw a saw? Time to leave.