I mean an injury penalty to Activity, Hurin, as taken from the critical tables.
Then yes, the activity penalty only applies to OBs and skills, not DB (unless you are parrying, in which case it applies to your weapon skill, as JDale noted).
The main things that can affect your Quickness DB are armor penalties and not being aware that you are in a combat situation (see 'Quickness Stat Bonus, 4.4.2, p. 13 of Arms Law). But injuries do not. This is clarified on p. 19, 'Critical Interpretations', 6.6.4, where, under '... at -#', it says, 'All of the target's bonuses
(except DB and RRs) are modified by this number...' [emphasis added].