Manual transmissions, hopefully this isn't a stupid question.

I've been watching a lot of performance driving videos to pass the time and seeing all the maneuvers that they do, while watching someone do a J-Turn, I just imagined a scenario in which I lost control of the vehicle and it threw me into a J-Turn, of course it the transmission would have to be placed in neutral then reverse to keep momentum going, but what kind of damage would occur if the transmission was left in say, third or fourth gear on accident? I would assume the transmission wouldn't let the wheels spin the opposite direction, and skid most likely? I'm trying to understand the mechanics of the transmission a bit more. Thanks! via /r/cars http://ift.tt/2u1YFfx