From LSWiki

   Class: Esoteric Skills
   Attribute: Perception
   Pedagogy: Procedural
   Practitioner Term: Practitioner of Combat Focus
   Specialty Required: Degree I
   Special Maximum: unmodified killer instinct skill, or unmodified tactics skill, whichever is higher
   Hidden Skill
   
   Practitioners of this skill are able to enter a state of focused attack and defense in which their attention is centered exceptionally
   strongly upon their target in combat -- that is, they are able to use the focused combat mode, a style of combat which benefits heavily
   from the use of combat advantage.  One's maximum capability at this skill is a product of one's skill at killer instinct and tactics.
   
   See Also: combat modes, set combat mode, combat advantage, killer instinct, tactics

Marcosy has stated that this combat mode gives more benefits outside of combat advantage.

Focused: In this mode, one stays focused on one's current target at the expense of other targets, with significant bonuses to both attack and defense against one's primary opponent. In general, this mode of combat prioritizes defense over attack, with highly precise strikes and careful parries and ripostes, and utilizes a judicious and measured pace to both build and retain advantage in combat. See 'help combat focus' for more information. You will attempt to defend against attacks so long as this leaves you with at least one attack in a given round. When you have combat advantage, you will lose it over time at an altered rate that varies with circumstance, typically more slowly than otherwise. When you have combat disadvantage, you will recover from it over time at an altered rate that varies with circumstance, typically quickly than otherwise.

Combat Advantage: This reflects transient benefits or impediments of positioning, preparation, and other tactical concerns. It can be gained (even by non-Hantaka) through "surprise attacks". Hantaka can also perform the feint maneuver.

Trainers

Guild required:
Hantaka: Hasan Wanders