Not sure how you were playing BF4 considering there's a handful of "WHy cant I play?" threads on the Battlefield boards. Might be that yours is a physical copy of the game and not digital? If PSN is down digitally downloaded games won't work properly because the lack of physical media means there's no choice but for PSN to verify the licence for the game on your account. This holds true for PS3 and PS4 I believe.