it happens when you stand still for a certain amount of time when using an axe (being a marauder). If you move you lose it. At level 20 you get a skill that lets you walk around without losing it but at a slower speed (so you can keep it up if your in a party between mobs i guess). I believe it increases parrying and evasion or something (and remember you get abilities that you can only use if you just parried). Hope that helps.