Migos Rapper: You Can't Pin Riot on Me ... Let Me Outta Jail!

Offset, the Migos rapper who's been locked up since April, is demanding his release ... saying prosecutors' "evidence" he stirred a jailhouse brawl just doesn't add up.

Prosecutors have been holding Offset without bail since his arrest for drugs and weapons charges, and at a previous hearing said he needed to stay behind bars because he sparked a jailhouse riot over the summer.

In new docs, obtained by TMZ, Offset says video footage from inside the jail shows no clear image of him, and only lasts for 20 seconds. His point -- even if it were him, which isn't clear, how could a RIOT only last 20 seconds?

Offset and his attorney will present their case in a bail hearing on Friday, which will be his FOURTH attempt at getting released. We're told they'll say there's no evidence to even support a trial, much less hold him without bail for 233 days.