I recently stated playing Martell.

My question is can Red Vengeance be stopped by Stark Boarderland keep?

As boarderland can only be triggered during a combat challenge.

Is Red Vengeance considered to be triggered during the combat challenge or after?

Look at the action window flow charts on pages 18 and 20 of the FAQ to follow this explanation. ( http://www.fantasyflightgames.com/ffg_content/agotlcg/support/LCGFAQ_3.1_Low_res.pdf )

There is a Framework Action for the resolution of the military challenge in question. The Framework Window has the following events:

1. Determine winner of challenge
2. Challenge result is implemented
3. Reward for unopposed challenge is awarded
4. Renown is awarded

Each event is broken down into (up to) six steps:

A. Framework Event initiates

B. Save / Cancel responses to Framework Event

C. Framework Event Resolves

D. Passive Abilities (if triggered) are resolved

E. Responses

F. End of Framework Event, Moribund cards leave play

Red Vengeance would be played in step B of the Framework Action Window for Framework Event 1 (The Save / Cancel responses step to the determine winner of challenge Framework Event.) So, yes, Red Vengeance is indeed considered to be played DURING the challenge, and Borderland Keep, being another Save / Cancel response would be played immediately afterwards, still in step B of Framework Event 1, which is to say, still during the challenge.

Long story short, yes Borderland Keep can be used to cancel out Red Vengeance.

Risc said:

Each framework event is very specifically NOT broken down into 6 steps. Each framework event cycles individually through A-C above, then moves on to a common D-F for all 4 of them.

This is hugely important. It means that while you play save/cancel effects (Step B) to each event individually, you have to wait until all 4 are complete before passives or Responses to any one of them. For example, you cannot play an "after you win/lose a challenge" Responses, like A Lannister Pays His Debts, until after claim, unopposed, and Renown are resolved. That means if you lose an intrigue challenge and have just the one card - ALPHD - in your hand, you're going to lose it to claim (in C-2) before you get a chance to play it as a Response (in E, which is shared by 1-4).

The point remains that you are "during the challenge" from the time the challenge is declared and attackers are knelt, all the way to the "End" step of the "resolve challenge" framework action window, though.

Thanks for the quick response guys.