System Reference Document

MELEE DEFENSE MODIFIERS 

Situation

Defense Modifier

Attackers in melee outnumber defenders

-1 for each net friend in the melee to a maximum of -4. (Leona, literally kicking and screaming, as well as biting, clawing, and spitting, is being mobbed by four orderlies. Because she's outnumbered, she suffers -3 to her DM.)

Defenders in melee outnumber attackers

+1 for each net friend in the melee. (In the above example, Leona will have a hard time landing a punch on one of the orderlies. All of them receive a +3 Bonus to Defense.)

Defender grappled

Defense is set to 5. Ignore other Defense Modifiers.

Defender grappling

-3

Attacker Charging

-2 to both the Defender for this one Attack and the Attacker for the duration of the Combat Round.