In fact, unless the head is uncovered, there is no chance the sap will
cause unconsciousness, although damage will occur if a hit is made.
An uncovered (or light-cloth covered) head struck by a sap has a 5%
chance per point of strength of the wielder to cause unconsciousness.
Strength greater than 18 means automatic unconsciousness;
ie., 18/01 strength is sufficient to cause this. A hit anywhere but on
the head will inflict half damage only and have no other effect.
 

Weapon Type	Approximate Weight in Pounds	Size S or M	Size L	Notes	Length	Space Required	Speed Factor	0	1	2	3	4	5	6	7	8	9	10
Sap	1	1-2	1-2	Sap	1/2'	1'	2	-14	-13	-12	-10	-8	-6	-5	-4	-3	-2	0

Q: Unearthed Arcana (page 78) says
that a sap will stun an opponent if it
hits him in the head when the head
is uncovered. Since there are no hit
location tables in the AD&D game,
how do you determine if the sap hit
the opponent?s head?

A: The DMG has a rule that says an intelligent
creature can aim a blow at an opponent
?s head half the time (1-3 on 1d6).
While this rule (see page 46) encourages
characters to wear helmets, I think it?s a
bit excessive. Try any of the following for
adjudicating attacks with a sap:
Any attack roll four or more over the
minimum score needed to hit the target
strikes the head. Strength bonuses don?t
count when determining the minimum
score to hit, but bonuses for rear attacks
(including a thief?s back-attack bonus) and
attacks on prone opponents do count.
Treat the sap as a pummeling implement,
and use the rules on page 107 of
Unearthed Arcana. The sap does no damage
unless a stun is scored. It has the
chance of a large and hard object to stun,
and does normal sap damage (1-2) when a
stun is scored. A sap is a weapon and
negates the initiative penalty for pummeling
attacks. Roll a 1d6 before each attack;
a one indicates that the attack will strike
the head if the sap hits.
(150.39)