Dodging and Parrying.
Each character has a Combat Penalty (CP) derived from calculating their encumbrance and subtracting their weight allowance. This number can be as low as zero, and the upper limit is the carrying limit for the character.
An opponent attacking the character adds its Combat Rating (CR), which is basically its hit points, to the characters CP to get a percentage chance to hit. Example:
A 5th level monster with 30 hit points attacks a 5th level fighter with 35 hit points.
The Monster has an AC of 6, a CR of 30, and a CP of 0, and a damage mod of +4
Fighter has an AC of 4, a CR of 35, and a CP of 20, a damage mod of +3, and a dex bonus of 10
The Monster has a 50% chance of hitting the Fighter, the Fighter has a 35% chance of hitting the monster.
The Monster will do an average of 5 points damage per hit against the fighter. (roll 5+4 on the damage chart)
The Fighter will do an average of 8 points damage per hit against the monster.
The Monster will do an average of 2.5 points damage per round against the fighter, killing him in 14 rounds.
The Fighter will do an average of 2.8 points damage against the Monster, killing it in 11 rounds, and taking 28 points damage during the fight.
The Fighter has other monsters to fight, and doesn't want to cut his odds that close. He has a few options:
1) ATTACK!: Use his dex bonus to hit, giving him an extra %10 to hit per round. This ups his to hit chance to 45%, increases his average damage per round to 3.6, and shortening the fight to 9 rounds, taking 22.5 points damage during the fight.
2) Dodge: Using his dex defensively, reducing his CP to 10, and reducing the monster's chance to hit him to 40%.
This reduces the monster's average damage per round to 2 points per round, and will take the monster 18 rounds to kill him. He will take 22 points damage during the 11 rounds it takes him to kill the monster.
3) Parry: Use primary or second weapon to block monster's blow
The second weapon can be a sword or a shield. If using a sword, normal "two weapon fighting" penalties apply. If using a shield with shield proficiency, there is a -10 to the primary weapon hand and no penalty to the shield. Shield stats are on the shield chart below:
We are going to give him a medium steel shield. This increases his Combat Penalty by 10 due to the weight, giving him a CP of 30, and upping the monster's chance to hit him per round to 50.
He now gets two "attacks", one with the shield, and one with the sword. The shield give him +10 to CR, so when he block with his shield his CR is 45. Using the shield detracts 10 from his sword arm, so attacks with his sword are at 25.
When he uses the shield, he subtracts the shield CR from the opponents CR. So the Orc is at a modified CR of -15. The orc now has a 5% chance to hit.
His CR is 25, giving him a 25% chance to hit the orc.
When using a shield for defense, if the opponent "misses", it automatically hits the shield. This reduces damage significantly, but does not eliminate it. Here's the chart for reducing shield damage:
Lets say the monster rolls a 5, and adds its +4, for a 9. The shield is AC4. The 9 reduces the effective roll to a -5. Damage is calculated on the normal damage chart below:
Keep in mind that with lucky rolls, the monster can do as much as 7 points damage per round, killing the fighter in as few as 5 rounds. If the fighter is lucky, he can do as much as 11 points damage per round against the monster, killing it in as few as 3 rounds. In fact, the fighter stuns the monster on a damage roll of 7 or higher, giving him a +20 to hit the following round, upping his chance to hit to 45% that round. The fighter should do quite well against the monster.