How does guarded Position work? Will every attack made on a target which played this card as his action get a black die, or 2 with the better success line? Or is it only one attack that gets this hindrance in its dicepool?

All of the attacks against you or your allies within your engagement gain the misfortune die (or dice).

Thank you! That is the way we played the card.

The "or your allies" part gets overlooked often, also.

It is a powerful card. My group uses it more often now, after me introducing it. If you have an engagement with 4 players in advanced or normal guarded position, with shields and advances parry/block/dodge, you will never land a hit. And that group has Riposte or Counterblow to kill your monsters. That is hardcore.

The card is basic so everyone gets it and has a recharge of tero, so can be played every round. The effect is cumulative for everyone in the engagement. What is not to love?

True, and with a decent discipline score, the non-combat head can be adding a challange dice to all incoming attacks and taking recharge tokens away as well. Double bonus. Of course, foolish over conservative players run the risk of delaying it and over zealous players will often break from otherwise very solid formations, so GM's often need not fear as much as they might think they have to.