The 'Combat' chapter in Psi World consists of seven pages; about two-and-a-half of which are dedicated to tables and details regarding weapons and accessories (including, inexplicably, ranges for communications equipment). Of the remaining four-and-a-half pages, one page is consumed by mostly repetitive outlines for unarmed combat procedures. The idea of presenting attack resolution rules in the form of an outline is a good one; however, several repetitions of that outline with minor variations is boring and unnecessary. The rules explain how to conduct a combat throw. After a successful throw, the attacker may attempt to pin or choke the target. The 'unarmed attacks' section concludes with how to conduct a normal strike. Readers would have been better served with an explanation of normal strikes first and foremost, followed by throws, pins, and chokes as special cases. If desired, complete outlines for each attack 'form' could have been printed on the GM screen (included with the base set) or the blank back cover of the rule book.
Psi World uses a skill-based system and it makes allowances for untrained attacks. I find the rules for untrained attacks more irksome than the rules for determination of hit points. Untrained 'skill levels' are determined by doubling the average of two attributes. 'Doubling the average' is pointless! Just use the sum of the two attributes. Dang.
Characters have a total number of hit points. Each of seven hit locations of the body (i.e., head, chest, abdomen, two arms, two legs) has a set number of hit points as well as a percentage of the character's total hit points. For instance, a leg has 4 hit points plus 10% of total hit points and the abdomen has 6 hit points plus 25% of total hit points. Damage from a wound is subtracted from both the hit location hit points and the total hit points.
A character who loses all of his or her 'total' hit points is unconscious and can only be revived through “professional medical attention.” If the 'total' number of hit points is negative, the character will die unless medical attention is received within a number of rounds equal to his or her Endurance score. (1 round = 10 seconds) When all of the hit points for a given hit location are depleted, that hit location is disabled; the effects vary based upon the specific hit location (e.g., a disabled leg halves the character's movement rate). Disabling effects are described on page 4 (in the character generation section) as well as on page 26 (in the combat section). In both places, a character loses consciousness when all hit points in the head hit location are lost; however, the duration of unconsciousness differs. On page 4, unconsciousness lasts for one hour plus an additional hour for each hit point taken over the hit location total. On page 26, unconsciousness lasts for 3d20 turns. (1 turn = 1 minute) Page 26 also explains that whenever a hit location is disabled, the character must succeed with a 'shock resistance' roll or suffer unconsciousness for 3d20 turns. The durations are cumulative, so – according to page 26 – a character with a disabling head injury and who fails a shock resistance roll will be unconscious for 6d20 turns. I would recommend the page 4 rules, forgoing shock resistance rolls for disabling head injuries.
A target's defense score is applied to an attacker's chance to hit. Therefore, it is beneficial to have a negative defense score. (Characters with an extraordinarily low Intelligence or Agility could wind up with a positive defense score.) Armor is presented as a negative number that supplements defense score. (Armor does not affect 'throw' attacks.) In addition, armor provides a percentage chance that damage will be halved, assuming the armor covers the applicable hit location. For instance, a motorcycle helmet provides “-5 on defense.” So the chance of success of an attack against a person wearing a motorcycle helmet is reduced by five (assuming the attacker is not specifically aiming at a hit location other than the head). If the attack is nonetheless successful and the head is determined to be the afflicted hit location, there is a 20% chance that damage from the attack will be halved.
Encumbrance is not an issue in Psi World and, as far as I can tell, there are no rules for falling or drowning.