Attacks of Opportunity
Attacks of opportunity occur when an individual ignores an enemy. The attack made is a free attack that is made immediately. An individual can make multiple attacks of opportunity in a round, but only 1 against each opponent in a round.
Number of attacks of opportunity
Warriors and Monsters: 3 + 1/5 levels/HD
All Others: 1 + 1/5 levels/HD
Surprised individuals cannot make attacks of opportunity
Attacks of Opportunity are provoked when:
Attempting Missile Combat (Except at the threatening character and only on the first round of them being threatened)
Attempting Spell Casting (Except at the threatening character and only on the first round of them being threatened)
Moving out of a threatened square (including 5’ step, move, charge, and run, but not Withdraw)
Turning so that the threatening individual is now in a rear square
Attempting unarmed combat against an armed foe
Threatened Squares: All squares in the individuals front within reach (1 for most M sized or smaller). Some creatures (like oozes) have no defined front and threaten all targets within reach of any side of them. Larger creatures or those with reach weapons (like polearms) extend their front facing squares
Getting Past Defenders:
If a character tries to sprint past defenders they incur attacks of opportunity, and their progress is stopped if a successful knockdown occurs or if a critical hit is scored.