Ellaborate friend
Maybe not unrealistic, but impractical in a real world setting... You have to remember you're wearing heavy gear on your body and a heavy sword plus maybe shield in your hands.
Now somebody is striking towards you which is an action performed in miliseconds and you're planning on dodging that by throwing your whole body to the ground, roll around and stand up again.
Not only do you lose sight of your opponent, giving him the opportunity to strike you just another time; you're spending way to much energy no this whole action which might not even be possible depending on the gear you're wearing. Your scabbard will stick out, you might lose your helmet, your chainmail armor might be warped.
And in the end you have gained nothing by this move. Ideally you would dodge in order to land a quick counter attack...