Normally, I trigger Throwing axe at 4.2.2

What if Catelyn Stark participating in the challenge?

Could I trigger The axe?

Specifically, from where to where Catelyn have effect?

(Throughout 4.2 to 4.4?)

Tks a lot.

Short answer, no.

Longer answer. Start with the definition of participating (rulebook p. 15). "Any character that has been declared as an attacker or as a defender for a challenge is considered participating in that challenge through the resolution of the challenge." Next go to the challenge phase (rulebook pp. 27-29). The throwing axe would trigger at step 4.2.2. - Compare STR to determine challenge winner. However, Catelyn is still participating in the challenge (and thus stopping you from using the axe) until step 4.2.6. - Challenge ends.

So no, you won't be able to use a throwing axe against her.

Thank you