Talk Fantasy Football

The rules state you can choose to add it to armour or injury but the way the 6th is worded. You can apply it after the dice is thrown.

If the armour roll fails by 1 you can use MB to get past it

but

If you pass the armour roll you can then apply MB to injury

It sounds like it is much more flexible to use.

If you do not use MB on the armour (read; you pass the armour without the MB), you can use the +1 MB on the injury.

Not on the Casualty roll

it says you can use it on the armour OR the injury, not both

unless you have the old 3rd edition rules where you could use it on both