Another mystery crash - WHY?! 

Good chance the tail hub came off before the crash and caused the tail issue.

I'm glad it's not just me that crashes a lot. Mine is usually user error though. I keep plugging away because I'm obsessed with these machines for some reason! Hope you work out what went wrong and get it back up in the air again soon.

I’d say you definitely lost the tail - hence the spin - hence the crash - because the screw holding the hub wasn’t secured properly with thread lock etc. You saw the hub was right off. That wasn’t crash damage. It couldn’t happen in a crash. It usually breaks the blades but hub stays on shaft.

Grub screw came loose on the tail shaft so you lost tail drive and it spun. Possibly no Loctite on the grub screw or it wasn't located in the dimple/flat on the shaft.

First of all, thank you for sharing. My take is that the grub screw which was holding the tail rotor hub onto the shaft got loose and thus making the shaft slip and ultimately disconnecting the hub. Although you didn't tell if you cleaned the machining oil off of the grub screw and used thread locker when tightening it down again, I'd like to point out, even if this is already beaten, that the tail section is "fake assembly". On mine, that very grub screw was soaked in machining oil. Tail belt skipping could have been a problem, but I don't know how many turns you used to increase tension. But it's still a new "tight" belt, which possibly doesn't need that much tension yet imho (?). Opinions on how many turns to use vary greatly reading the forums and youtube. Mine is moderately tensioned. Best of luck figuring out the cause to avoid this from happening again.

Tail failure -screw of tail hub need therd lock. check screw before and after flight everyday you fly. -check all mechanics and servo

esc may have shorted a hard landing on the skids can bend the bord and stretch the wires

loss of tail rotor efectivness

Any reason you fly over hard ground instead of grass? Could have been easier crash potentially on softer ground/grass. This is coming from someone that regularly fly over a pond and kill all electronics :). I should take my own advice :).

That's unfortunate, hopefully you find out what it is or something.

Very bad. But shit happens.... I have sometimes the same problem with my helicopter or plane. Dont understand it, nothing wrong. Sometimes its going crazy. Dont know why. Kost me a lot off time, money And waiting on spare parts. Succes