Slack Line Trophy

I recently finished the story for SM2, and i’m just now finding out about the slack line trophy since i’m working forwards platinum (it’s my last trophy needed). I was wondering if it was possible to stealth take down enemies in the random street crimes that appear when you swing around? I tried lots of times but can’t. Btw i never manually saved any progress (idiot) / if there’s any other way to do so

Thanks !