What's the timing on this? Is it when you're declared as a defender or after they have chosen their weapon?

I.e. If you jam their lock can they still shoot their proton torps?

8 minutes ago, FriendofYoda said:

What's the timing on this? Is it when you're declared as a defender or after they have chosen their weapon?

I.e. If you jam their lock can they still shoot their proton torps?

It is before dice a rolled, after the weapon is chosen. The requirement of a lock for certain weapons, or focus for others, is when the weapon is chosen. You could jam their lock but they would still shoot the chosen weapon (and could not change which weapon they shoot).