Frenzied troops gain +1 Attack and the Immunity (Psychology) special rule (explained later).
Berserk Rage
A unit that includes one or more Frenzied models can only choose Hold or Stand & Shoot as a charge reaction.
If, during the Charge sub-phase, a unit that includes one or more Frenzied models does not declare a charge, then it must do so unless a Leadership test is passed. If the Leadership test is failed, the Frenzied unit must declare a charge against the nearest viable enemy.
A unit that includes one or more Frenzied models that attempts to restrain pursuit if it beats a foe in close combat suffer a Leadership modifier equal to the result they won the combat against that unit by. For example, if the Frenzied unit won the combat by 3 and the enemy unit flees, the Frenzied unit suffers -3 to its Leadership if it attempts to restrain from pursuing. Note that in case the enemy unit was completely wiped out, the Frenzied unit can choose whether to overrun or not as normal.
If a model has the Frenzy special rule from two or more different sources (such as a combination of different special rules, spells or magic items), it gains +1 Attack. However, they must always pursue, with no chance to restrain.
Losing Frenzy
Unlike other special rules, Frenzy can be lost as the game goes on. Models retain their Frenzy for the entire game unless beaten in combat, at which point the enemy have succeeded in knocking them into a less fanatical state and the Frenzy (together with all associated rules) is lost.