You have to beat the three first gymleaders, then you can go back to fight your father Norman in Petalburg .
the fourth gym is in celadon city at the bottom left of the city. the gym leader is erika. the badge is called the rainbow badge
Beat the Gym Leader
The fourth gym.
Go to the forth gym!
Lavaridge town is where you get the fourth badge in ruby.Hint:the gym leader uses fire types so use a water type.
Defeat Flannery the lavaridge town gym leader.
misty
by beating the fourth gym leader
Flannery's gym in Lavaridge Town.
you have to beat other gym leaders before you can get your hearthome city badge, lol. it's probably the hardest badge to get.
The 4th pokemon badge is given by Erika the Celadon City Gym Leader.
Flannery, a fire type gym leader.