There has always been Stam damage in UO, it just wasn't significantly noticable recently, unless you're taking real heavy hits.
Macers used to be renowned for their ability to wreck people's Stamina (as well as Armor), and were feared for it. Whenever a Macer walked onto the battlefield, all other Warriors gave him a wide berth, out of fear of having their Stamina and armor obliterated by his Warhammer or War Axe. Even Mages feared Macers, for a Macer with a Q-Staff could not only rapidly interrupt spell casts, but also completely annihilate their Stamina, making the Mage unable to run or flee, and therefore, a sitting duck.