Acrobatics is a skill that allows Graceful Roll, as well as combat damage negation with the passive skill "Dodge". In combat.
On United Factions we have disabled these Acrobatics skills of mcMMO, as it would form a threat to the PvP experience.
The skill is simply too overpowered to be rolled out. The impact of this skill between experienced players and new players would be so significant that new players would not even attempt to PvP with an experienced player. The battle for the experienced player would not be much of a challenge either, making the outcome of PvP fighting ridiculously predictable.