I found that when you are figthing something (in melee) and press shift then your character do a block animation,
i was searching on forums but didnt found anything about this mechanic or just a relic animation.
Its do anything?

It is kind of resisting damage or something like that. If I remember right you can see your stats changing when you hold Shift and it is maybe in Sacred 2 too? It was quite a long time ago for me.

Pressing this key will increase your Defense value significantly for as long you hold it, effectively decreasing enemy hit chance against you.

Yep just testing on my level 6 character his defense goes from 46 to 131 holding the block defense shift key, so gives a good boost in defense.

I haven't ran into any situation yet that requires this, but im guessing against harder foes with easy to see attack animations you'll be able to "block" as they are trying to hit you then can attack after.. Not sure if the increase is a percentage or a fixed amount yet, haven't looked into it that much.