A friend who does not reload has been saving his indoor range brass. He sweeps it up and bags it but I also got a few oddball pieces of brass he does not have guns for. It was mostly 9mm. He does not reload so he gave it to me. I sorted and threw the 9mm in the tumbler expecting to inspect it after it got cleaned.

Brass looked good but I found one piece with the live primer in upside down. No bullet. I get how that can happen to a reloader but how does this end up on a range like that? Someone decide to leave a reloader a turd bomb hoping they would just pop it in the reloader and possibly set it off? It deprimed with no incident but got me wondering if it could be set off with nothing supporting the anvil. And to the fist point, how does it make it to the range?

May be came from factory loaded ammo like that. When it didnt fire or was seen the person pulled the bullet?

My thought exactly. Not sure how it would happen but if it did then it's easy to see how one can forget about the live primer in lieu of the spilled powder.

I like your use of "turd bomb" here. it made me smile!

I have seen reloads and factory ammo with primers backwards but at least they had a bullet seated in them. I suspect someone that did not know you can remove the primer that is in backwards easily dropped it on the range to get rid of it.