That post is locked in or cross threaded probably which has caused your T nut to come undone. Take a pair of vice crips and lock them on the nut and remove the post. You will need to pick up a new t nut. I get them at the hardware store. They aren't very expensive.

I just clamp down with the vice grips and if the bolt breaks I buy a new one. If you are stripping the playfield you will be placing an order anyways

That's true on the ones that are not available. I take for granted some of these post types not being available because I picked a bunch up off of stripped out playfields a while back. Pretty much every post I have ran across on system 11 are available through Marcos though.