Stamina
From Ultima Online Forever Wiki
Description
Stamina is one of the three stats that your character utilizes with it's skills along with Mana and Hit Points. Stamina is determined by the level of Dexterity which translate into your characters total Stamina. Stamina is depleted when your character takes damage, attempts to move when holding more than their maximum carrying weight or when your character passes through another character.
An enemy with Macing who strikes you with their mace can reduce your Stamina more so than other weapons or weapon skills. Stamina is also required for characters who choose to Stun and enemy. Stamina is the third bar represented on your characters status bar in the interface.