Play video content EXCLUSIVE

TMZ has footage of "Kony 2012" honcho Jason Russell in the midst of his naked meltdown in San Diego ... pounding his fists in anger and screaming maniacally. [UPDATE: TMZ has obtained a close-up video from Russell's meltdown. CLICK HERE to see.]

As we previously reported, Russell was detained by police yesterday ... after witnesses say he was running around naked and making sexual gestures.

Russell was held on a 5150 psychiatric hold ... so authorities can decide if he poses a danger to himself or others.