Referring to someone who is opposed to the existing system (the establishment).(adjective)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "anti-establishment" in a sentence
"And all those so-called anti-establishment flea party democrats will get steamrolled by the super-rich Democratic Party and its PR machine hope and change!"
"She chances upon a coterie of anti-establishment merry pranksters who live in the Haight-Ashbury and decides to spend the night with them."
"What makes the Jack Flash sequences arguably escapist is not just their gaucheness but the vicarious thrill of his anti-establishment rebellion."