During a concert of Katy Perry's, Selena Gomez, who is present backstage and in the audience, claims that the song 'Roar' sung live is Katy's weakest performance ever, and that she would find it quite easy to sing Katy's song much better than Katy does herself.
As Selena announces that onstage over a microphone Katy is surprised at the girl's immense provocation - however, self confidently she finally challenges Selena to a singing contest in which both women sing 'Roar' successively and the audience will decide who is better.
Katy knows how much there is at stake for her: If she gets upstaged by Selena singing her own song better than she does herself she will be the laughing stock of the pop music world and it will take her a long time to repair her damaged image and dignity.
Selena also knows: If she's unable to prove her claim that she can sing Katy Perry better than Katy herself, getting defeated by her, it will do immeasurable damage to her career and set her years back in her struggle to make it to the top.
Katy goes first and performs her song 'Roar':
http://youtu.be/fmkasyyO9z4...Then, Selena comes on stage, mockingly claps her hands in applause to Katy, and seconds later throws herself into her cover of Katy's song, giving everything she can in order to outsing and humiliate her:
http://youtu.be/7UAO83mEPcsAfter the contest, the confrontation between the two women is not over - in their shared dressing room, the winning lady ridicules the mortified losing one until it becomes clear they still have to settle things between them...
Katy and Selena soon begin to replace an initial vulgar trash talk by slapping each other's faces, and when both women have their cheeks burning with resounding, stinging blows they grab each other's hair and pull with all their strength, each trying to force the other to the floor to pin and defeat her...