B368
GURPS Martial Arts pg 107 under Move and Attack mentions the following:
- The GM should consider extending the -2 for “trying to do two things at once” to all success rolls except defense and resistance rolls against enemy attacks.
- For instance, it would modify DX rolls to evade or to keep someone from evading you
This clarifies that even though evasion/obstruction is resolved via a quick contest, neither is considered a defense roll or a resistance roll.