In the end this is our fault, but a guy came in wanting to try us out. We got him on the mat and we're showing him some throws, dude labds on his back and is in pain. Gets up and says he had lower back surgery.... Why in the world would you think "let's try learning martial arts now before I am healed up."? So he left and said he'd come back later. We forgot to ask about any medical issues first but it was assumed he was fit for it since he volunteered himself.