Oakland Athletics fans flocked to the Coliseum on Tuesday to hold a "reverse boycott" against the franchise's plans to move to Las Vegas ... and the movement got support from one major supporter -- Green Day frontman Billie Joe Armstrong!!
More than 27,000 supporters -- the biggest crowd of the season -- filled the stadium to prove to A's owner John Fisher they still support the ball club ... and many wore shirts calling on him to sell the team.
Of course, A's fans have been fed up for years .