Try to get around him.

The brutish orc bellows and begins to lumber forward, holding the shield up as he charges towards you. Waiting for the last moment before he swings the mace, you dart to his right, trying to get outside the arc of the swing and expose his unprotected side to your blade. Unfortunately you moved a moment too soon and the attack comes not from overhead as you expected but swings around to follow you. The giant mace, with all the power of the orc's ferocious muscles behind it, catches up and sweeps your legs out from underneath you. You fall backwards, flipped down onto your shoulders, the back of your head striking the ground.

You must keep moving. You try to roll over onto all fours, but your shattered legs can bear no weight. Collapsing onto your side and reaching for the sword, inches from your grasp, your vision is filled with an armoured boot stamping down just in front of your face, pinning your arm below the shoulder and probably breaking those bones too. You can feel nothing due to the adrenaline, but you see the metal banded edge of the shield coming down towards your face and lose consciousness in an instant as the blow shatters your skull.