In the Expert rule book (page X25) it states:
Characters who engage in combat without a weapon (for whatever reason) will do 1-2 points of damage plus and strength adjustments for a successful attack. All normal rules regarding combat apply to unarmed combat.
So that does it for punching and kicking but what about grappling where your character is trying to grab or wrestle down an opponent?
I have typically used one of the following methods:
Method 1. Opposed d6 rolls. I think this is from OD&D, maybe an issue of Strategic Review or an early Dragon. Each side rolls a number of d6s equal to the HD or level of that side. So for example, a 4th level fighter is being grappled by 5 orcs. The player rolls 4d6+strength adjustments and the DM rolls 5d6 for the orcs (there are no strength adjustments as strength is factored into HD). High side wins.
Method 2. The Ode to Black Dougal Default System. Have the player roll 2d6 with some adjustments for relative sizes, strengths, circumstances, etc.
2= it turns out REALLY bad for the player
3-5 = it turns out bad for the player
6-8 = neutral
9-11 = it turns out well for the player
12 = it turns out REALLY well for the player
Using the Fiendish Dr. Samsara's example of a Sorcerer, finding himself not too successful with spell or weapon, wants to pull a beastie off a companion before it eats her shoulder. Roll 2d6 with some adjustments you feel are appropriate:
2 = It turns out very poorly for the sorcerer - maybe he is knocked down at the feet of another beastie
3-5 = The sorcerer fails to grab the beastie
6-8 = gets his hands on the beastie but doesn't pull him off. May allow for a bonus to try again next round.
9-11 = pulls the beastie off
12 = pulls the beastie off and punches it in the face!
Method 3. Probability of Success. I have been gaining a greater appreciation for this style lately. Just determine what the probability would be for the characters to succeed and roll the d%. Using the sorcerer example again, after weighing many factors the DM decides that the sorcerer would have a 30% chance of grabbing the beastie and pulling it off his companion.
How do you do grappling in your old school game?