Flanking
Position in combat matters: A character that is surrounded is in significant trouble.
A character is said to be flanked if they have opponents on opposite sides of themselves. If a line can be drawn from the center of one opponent's square to the center of another's, and it passes through either opposite corners or opposite edges of a square containing a character, that character is flanked.
In the illustration below, a line can be drawn from the square containing Eldrin Stormscale to the square containing Sir Roland, and it passes through opposite corners of the square containing the Guard. The Guard is flanked.
A line drawn from the square containing the Guard to the square containing the Assassin passes through the square containing Sir Roland, but it does not pass through opposite sides or corners. Sir Roland is not flanked.
A character that is Flanking an opponent gains favour to any melee attack roll made against that Flanked opponent. Ranged attacks do not gain favour against a Flanked character. A character that is not Flanking an opponent does not gain favour against that target if the target is Flanked by anyone else.