Berserker (GURPS) is one of Fallout GURPS disadvantages. See: Fallout GURPS.
You tend to lose control of yourself under stress, making frenzied attacks against whoever or whatever you see as the cause of the trouble. Any time you take more than 3 hits in one turn, you must roll vs. IQ. A failed roll means you go berserk. Other conditions of extreme stress (GM's option) may also require an IQ roll to avoid berserking. A berserker may deliberately go berserk by taking the "Concentrate" maneuver and making a successful IQ roll.
While berserk, you must make All-Out Attacks each turn a foe is in range, and Move as close as possible each turn no foe is in range. While berserk, you cannot be stunned, and injuries cause no penalty to your Move score or attack rolls. When your HT falls below zero, make a HT roll each turn; you do not fall until your body is totally destroyed (-10 HT) or a roll is failed. You then fall unconscious - or, if your HT is fully negative (-1 HT), dead! If you snap out of the berserk state, all your wounds immediately affect you, but no further HT rolls are necessary; if your HT is below 0, you simply collapse.”— Steve Jackson Games GURPS sources
With the abandonment of GURPS, Berserker (GURPS) was removed, image reused for the kill counter.