Armor check penalty

Armor Check Penalty (ACP): The Penalty to Skills due to the restrictiveness of certain armor.

The following are subject to ACP:
 * Balance
 * Hide
 * Jump
 * Move Silently
 * Tumble
 * Swim is subject to double the standard ACP

Carrying capacity also can cause an ACP.
 * Medium encumbrance causes a -3
 * Heavy encumbrance causes a -6

It is believed that Turbine did not incorporate the Carrying capacity as written in PnP. Furthermore, there are times when your ACP-related skills will drop unexpectedly. The game will not tell you that you are encumbered as you are not at the level of "Overloaded", however, your skills are already suffering. This has been known to appear like a bug and is most commonly noticed in relation to Swim because your breath will drain at an incredible rate.

Non-proficiency with a certain armor or shield will apply the ACPs to all attack rolls, Strength based skills and Dexterity based skills. Non-proficiency penalties from armor and shields stack.