According to Adam Schefter
Pro Bowl cornerback
Nnamdi Asomugha's contract voided and he will be allowed to become a free agent without the Oakland Raider being able to use their franchise tag on him, according to an NFL Players Association document. Asomugha’s deal included a little-known clause that said his contract would void if he didn’t achieve his not-likely-to-be-earned incentives in 2010 -- and he didn'’t.
NFLPA document: Nnamdi Asomugha of Oakland Raiders a free agent - ESPN