Player's Handbook[]
The character is practiced in all manner of acrobatics—dives, rolls, somersaults, handstands, flips, etc. Tumbling can only be performed while burdened with light encumbrance or less. Aside from entertaining, the character with tumbling proficiency can improve his Armor Class by 4 against attacks directed solely at him in any round of combat, provided he has the initiative and foregoes all attacks that round. When in unarmed combat he can improve his attack roll by 2.
On a successful proficiency check, he suffers only one-half the normal damage from falls of 60 feet or less and none from falls of 10 feet or less. Falls from greater heights result in normal damage.
Player's Option: Skills & Powers[]
Tumbling: Characters with this proficiency can roll, somersault, stand on their hands, flip forward and backward, and otherwise perform feats of acrobatics. They can only perform tumbling feats if unencumbered or lightly encumbered.
Tumbling characters can improve their AC by 4 on a given round if: they avoiding attacks directed against them, win initiative, and elect not to attack that round. A tumbling character can move up to 20 feet, or remain in one place, during the course of this evasion. In unarmed combat a character with tumbling ability improves attack rolls by +2.
The character can attempt to dodge through obstacles or escape through narrow apertures, but successful proficiency checks are required. If the character topples from a height of 60 feet or less, a successful proficiency check results in suffering only half damage from the fall.
The Complete Barbarian's Handbook[]
In most cases, a barbarian won't use the tumbling proficiency for entertainment purposes. Instead, he uses it to elude and confuse enemies. He gains the Armor Class improvements, attack roll; bonuses, and damage reductions from falls described in the Player's Handbook.