This skill is a Special Rule that is only available to specific Star Players. Please visit this page to find a list of current and past Blood Bowl Star Players.
Crushing Blow
Once per game, when an opposition player is Knocked Down as the result of a Block action performed by Zug / Varag, you may apply an additional +1 modifier to the Armour roll. This modifier may be applied after the roll has been made.
Crushing Blow is one of the more mundane special rules, in some games it might never come into play as you either beat the opponents armour without it, or you roll much lower than their armour value where this would then let you then break it.
You can combine it with Might Blow (+1) which will let you break the armour when you roll one less than the opponents armour value. Ideally though you want to use the Mighty Blow bonus on the injury roll to increase the odds of the player getting removed from the pitch.
If it’s the opposing team’s best player then maybe you add them both to the armour roll, especially if they are hard for you to knock over. Otherwise I would save it for when you equal an opponents armour, use Crushing Blow to break the armour and get the Mighty Blow on the injury roll.
One last factor to consider would be how many more armour rolls you think you are likely to get from Mighty Zug. If you’re playing an agility team who are just going to try and minimise base contact, you might be better off blitzing with one of your ordinary players who has Tackle to combat their Dodge players. In those types of games then maybe just use Crushing Blow at the first opportunity even if you need to use Mighty Blow on the armour roll as well. If you’re playing against a slower bashing team where both teams might see a lot of players marking each other, then you might find more opportunities for Zug to be knocking opponents over.