With the new attack for affect or block actions (PRC 3.1.4) there should to be a new skill.  This skill should be perception based and be called tactics or situational awareness, it is the skill used to try and flank someone or push them onto unstable ground.  It is both the attacking skill and defensive skill.  If this was PRC 4.0.X or in between campaigns I’d just create that skill.  However retroactively creating such a fundamental combat skill causes problems with existing character builds.

I considered various options, but in the end decided to overload notice with the tactics functionality until such a time as I feel the need to create a version 4.0 or I start a new campaign.