“You hear my voice, your hear that sound
Like thunder, gonna shake the ground
You held me down, but I got up”

Katy Perry – Roar Lyrics on LyricsMode
She's standing up for herself, because he uses her and pushes her down. But then she began getting up and began ignoring him. And she fights her own battles. That's what it's about. Standing up instead of being used and pushed around.