Rear wheel slipping out of slot after attempting a 180
If the rear wheel is moving in the dropouts, its because the forces applied to the axle are larger than the clamping force of the retention system.

You say its a Quick Release - the lever should require enough force to close that it leaves a mark on your skin.   If you can't get it to tighten enough beforehand, the QR may have stretched and come to the end of its thread.  If so, replace the whole QR and nuts.

Even then the QR's acorns may not be gripping the frame properly.  Take the wheel out and clean all dirt and grease and oil off the dropouts, both inside and outside and in the slot.  Then look closely at the serrations under the skewer nuts and make sure they are not smoothed off.  I've repaired one using a small triangular rats-tail file and a lot of patient hand filing... its a hardened steel surface and takes effort.

For sheer holding power, nothing beats traditional hex nuts.  If you're going to be exerting these forces on your bike then consider replacing the axle with a solid axle, and fitting some beefy wheel nuts.  Sounds like you're stunting, you may consider fitting pegs at this time - Pegs don't work with QRs at all.

Finally - you mentioned in a comment that the brakes are both broken, which is why you removed them and are now riding brakeless.  This suggests that your riding style is hard on the equipment, and you might be better off purchasing a more-robust stunt bike. 

You should cease riding this bike until the brakes are fully operational again.  It may be inconvenient, but too bad.  Your safety, AND the safety of others in the roadway is not to be compromised for your convenience.   


  DON'T RIDE A BIKE WITHOUT WORKING BRAKES !