There are only a few explanations for this. You think your boots fit perfect and feel very comfortable but in reality they are a bit big which is no problem it happens to everyone (but kinda is a problem cuz of shinbangs and you gotta buy new boots) Can you lift your heel at all when their buckled, loose feeling in your foot anywhere, does your boot hurt your foot anywhere else, do you loose toenails, are your feet cold when it's not like super cold outside, lets say higher than like 20 degrees, or anything else? Other explanations are you don't buckle your boots tight enough and your feet slide around, you buckle your boots so tight that they cut off blood circulation and wreck your shins. You have hairy legs and the hair on your shins rubs up against the boot and ends up rubbing off because of all the friction with the leg hair and boot leaving a bruise. You land in the back seat when learning new tricks like you said, but you just have got to learn to backslam on the ground instead of resisting and landing backseat, for example when you see those bosses on TV or in general sending like a 30ft cliff and they land with their backs literally smashing the floor, it is to prevent this as well as other stuff.
