Overrun

When a larger creature attempts to move into a smaller, standing enemy's square, it is called an overrun. Mounted figures use their mount's size for this purpose, so a human on a size L horse can overrun a human on foot. Overruns create an attack of opportunity for the figure being stepped on. After the defender's attack, the defender must roll a successful saving throw vs. paralyzation or be knocked down. Even if he does successfully save, he is forced one square away from his current location. This save is modified by a -4 penalty for a creature two sizes larger than the defender, a -8 penalty for a creature three sizes larger, etc.

For example, a halfling (size S) gets in an ogre's way. After the halfing's attack of opportunity, he must roll a successful saving throw vs. paralyzation or be knocked down. The ogre is two sizes larger, so the saving throw is rolled with a –4 penalty. Even if the halfling successfully saves, he is forced out of the square.

When a defender is knocked down by an overrunning creature, he may suffer a trampling attack. The trampler gets an attack of opportunity that inflicts 1d4 points of damage per difference in size. Even though the defender is prone, no modifiers apply; trampling is an afterthought on the attacker's part. The DM can adjust the damage as he sees fit; very dense creatures such as clay or stone golems may not be seriously hurt by even a giant's trample.

Continuing our example, the halfling fails his saving throw and is knocked flat by the ogre's rush. The ogre gets a free attack of opportunity and rolls a hit. Since there is a two-category difference in size between them, the halfling suffers 2d4 points of damage. Being trampled by someone ten times your weight can be lethal.

A prone creature with an enemy in its square may get up by using a full-move action. Since two standing enemy figures cannot occupy the same square, size always wins; the larger of the two creatures displaces the smaller one. In addition, the standing figure always chooses which square the displaced figure enters. If the creatures are of the same size, an opposed Strength roll is made to determine who stays and who is displaced.

Concluding our example, the halfling decides to rise again to avoid getting trampled some more. Since the ogre is larger than the halfling, the halfling must be displaced one square in order to rise. Since the ogre is also the standing creature, it decides which square the halfling is displaced to. If the roles had been reversed, with the halfling in the square of a prone ogre that wished to stand, the halfling would still have to be displaced, since it is smaller. However, this time the halfing, which is the standing figure, chooses which square to be displaced to.

Of course, the standing figure might wish to keep the other figure from rising, or the prone figure might decide to fight it out rather than try to rise. If one figure wishes to keep another figure prone, an overbearing attack is necessary, but treat the situation as if the attack roll to hit AC 10 is automatically successful (see Overbear).