actually it was way more common in European combat to use shield as offense than to kick. I dont think people realize how offensive shields were used back in the day, not so much "bashing" like using your shield as a giant "backhand" its hard to generate much power with our small rotation muscles as to make that very effective. now punching with the rim of your shield toward and enemys throat/face can cause tremendous damage. there are even accounts of opponents hurling their shields frisby style at an opponent and let me tell you that HURTS, lol I had a shield thrown at me(frisby style) by an amateur friend, hit me in the mid section and gave me a fractured rib lol. another account is throwing your shield at the legs of an advancing enemy to trip him up, Now im not saying its a great Idea to throw your shield away but it did happen then, then you have shield binding where you pretty much grapple using your shield to tie up and control your opponents shield, though this is obviously more of a defensive
maneuver. shield techniques were much more evolved than just "you attack and I block.." as far as kicking goes It can be effective but anything that puts your limbs out in the open is kind of risky, anytime anyone has ever tried to kick me ended up with a bruise on their leg lol, its just to easy to stepback and counter, If a kick lands in center of shield it doesnt do much if anything, if that same kick is landed closer to the edge of the shield it can leave the defender wide open because of all the leverage going against him, also a huge majority of the injuries back then were to the head and legs, telling us that the legs were in danger enough without throwing them at our opponent, or lol I guess it can say that people kept trying to kick and never learned.