Sacrificial

*Sacrificial Block
*Sacrificial Dodge
*Sacrificial Parry
in 2006 at http://forums.sjgames.com/showpost.php?p=181609&postcount=8 PK suggested a minimum penalty of -4 to defense if you were able to block or parry for an ally without taking the All Out Defense maneuver and first succeeding in a Sacrificial Dodge so that you were the target and then using your 2nd defense to parry or block for yourself.
Perks in GURPS Martial Arts offset this suggested -4 penalty and allow people to perform sacrificial parries or blocks without penalty:
*Shield Wall allows sacrificial blocks to anyone in side hexes
*Sacrificial Parry allows sacrificial parries to anyone in range of your weapon in any direction
*Teamwork allows sacrificial parries or blocks to teammates behind you (they must also have the teamwork perk, and this is defined as a narrow group) amongst other benefits.