The combat sports world is rallying behind Cain Velasquez ... with huge names like Dana White, Khabib Nurmagomedov, Henry Cejudo, Kamaru Usman, Rey Mysterio, and more calling on the judge in the UFC legend's case to let him out of jail.
TMZ Sports has learned over 30 people -- many famous -- penned letters to Judge Shelyna Brown asking her to let Velasquez post bail, which would allow him to mount his defense from home, not a cell.