Glancing blow

A Glancing blow is an additional hit caused with a two-handed weapon. Glancing blows initially have lower chances of hitting and do significantly less damage than ordinary attacks, but they can hit multiple enemies.

Glancing blows are an inherent property of all two-handed weapons, including quarter-staffs. No Feats or Enhancements are required to enable them, though some make them better.

Basic mechanics
One free glancing blow attack is made automatically against all enemies in a wide arc in front of your character on the first and fourth swing (if you have a fourth swing) of your attack sequence. You must be stationary,otherwise if you move while attacking, then you don't get Glancing Blows. It is possible -- in fact, common -- to get both a glancing and a normal attack against your main target. These are rolled separately.

Glancing blow weapon damage, and chance of applying special weapon effects can be increased by the Two-Handed Fighting feat line, by some Fighter enhancements, Barbarian enhancements, Half-Orc, and Warforged enhancements.

Glancing blow attack rolls use all your normal attack modifiers plus a -5 penalty.

Glancing blow weapon damage has a minimum of 1, however Damage Reduction applies against it normally, and can reduce the damage to zero.

Glancing blow weapon damage starts at a base of 20%, and can be increased by the Two-Handed Fighting feat line, and Barbarian enhancements.
 * Two-handed weapon damage glancing blows starts at a base of 20%.
 * The feat Two-Handed Fighting adds 10% weapon damage to glancing blows.
 * The feat Improved Two-Handed Fighting adds 10% weapon damage to glancing blows.
 * The feat Greater Two-Handed Fighting adds 10% weapon damage to glancing blows and additionally grants a glancing blow on your third attack while standing.
 * The Barbarian capstone Barbarian Might adds 10% weapon damage to glancing blows.

Glancing blows ordinarily do not cause any special weapon effects, but will do so at some percentage if you take any of the Two-Handed Fighting feat line, Kensai Specified Weapon Mastery I & II, Frenzied Berserker I, II & III, the capstone Barbarian Might, Orcish Great Weapon Aptitude, Warforged Great Weapon Aptitude Enhancements.
 * Two-handed weapon special effects glancing blows start at a base of 0%.
 * The feat Two-Handed Fighting adds 3% chance to produce special weapon effects on glancing blows.
 * The feat Improved Two-Handed Fighting adds 3% chance to produce special weapon effects on glancing blows.
 * The feat Greater Two-Handed Fighting adds 3% chance to produce special weapon effects on glancing blows.
 * The enhancement Greater Two-Handed Fighting adds 3% chance to produce special weapon effects on glancing blows.
 * The enhancement Kensai Specified Weapon Mastery I adds an increased chance to produce special weapon effects on glancing blows.
 * The enhancement Kensai Specified Weapon Mastery II adds an additional increase chance to produce special weapon effects on glancing blows.
 * The enhancement Frenzied Berserker I adds 2% chance to produce special weapon effects on glancing blows.
 * The enhancement Frenzied Berserker II adds 2% chance to produce special weapon effects on glancing blows.
 * The enhancement Frenzied Berserker III adds 2% chance to produce special weapon effects on glancing blows.
 * The capstone Barbarian Might adds 5% chance to produce special weapon effects on glancing blows.
 * The enhancement Orcish Great Weapon Aptitude I adds 2% chance to produce special weapon effects on glancing blows.
 * The enhancement Orcish Great Weapon Aptitude II adds 2% chance to produce special weapon effects on glancing blows.
 * The enhancement Orcish Great Weapon Aptitude III adds 2% chance to produce special weapon effects on glancing blows.
 * The enhancement Warforged Great Weapon Aptitude I adds 2% chance to produce special weapon effects on glancing blows.
 * The enhancement Warforged Great Weapon Aptitude II adds 2% chance to produce special weapon effects on glancing blows.
 * The enhancement Warforged Great Weapon Aptitude III adds 2% chance to produce special weapon effects on glancing blows.

Also worth to consider this:

Glancing Blows no longer scale with Base Attack Bonus, and start at a base of 20% weapon damage.

Enhancements and feats that modify the Glancing Blow damage multiplier now function.

The Two Handed Fighting chain has been modified to add 10% to glancing blow weapon damage per tier, and the chance to produce special weapon effects has been increased to 3% per tier. They no longer grant to-hit bonuses for Glancing Blows.

The Barbarian capstone, “Might”, now correctly grants +10% glancing blow weapon damage and 5% chance to produce special weapon effects in addition to its +2 Strength bonus. (A half-orc or warforged barbarian with all three THF feats, Great Weapon Aptitude, and Might will have deal 60% weapon damage with their glancing blows, with a 20% chance to produce special weapon effects.)

The Frenzied Berserker and Great Weapon Aptitude enhancements now give full information on their effects on two handed combat. link: http://forums.ddo.com/showthread.php?t=274230