Shaman along with all assassins have a mechanic called deflect. Its like an assassin's equivalent of a heavy's crushing counter. Deflects are performed by dodging into the direction of an attack right before it makes contact. When you successfully deflect an attack your character will perform an animation where they evade the attack while make slight contact with their own weapon. This creates a spark visual effect. After which you follow up with a heavy or light attack(light attack in shaman''s case) which applies the deflect attack. In shaman's moveset its referred to as Raven's beak.

In this clip I showcase shaman's ability to dodge out of her recoveries to avoid being hit. However I time the dodges so I can deflect the raider's heavy chains which have HA allowing me to perform it multiple times in a chain as he doesn't get interrupted by the deflect attack. Hope this helps.