D&Dtools1

Benefit

You ignore the penalty for hampered melee when fighting in a narrow space (an area smaller than but at least one-half of your space) or a low space (an area shorter than but at least one-half of your height) with light or one-handed melee weapons. Furthermore, you take only a —4 circumstance penalty when using a two-handed weapon in such conditions. In a space both narrow and low, you function as if only one of those conditions applied (see Chapter 7: Exploring the Underdark for rules on fighting and moving in cramped spaces). In addition, when fighting in cramped quarters, you do not lose your Dexterity bonus to Armor Class.