Avril Lavigne generally gives off a tough-as-nails vibe, but she's not 100 percent unflappable. While performing in China, the "Sk8er Boi" singer became so startled by something that she fled from the stage, right in the middle of a song. Her exit can be seen at the video's 3:54 mark.
She was singing "I'm With You," when something startled her, causing her to yelp and run backstage. On celebrity forum Oh No They Didn't, there's no consesus as to exactly what happened, but many believe that an overzealous fan attempted to climb onto the stage.
Lavigne's bandmates were startled by her exit, but quickly recovered and continued the performance, sans singer.
As Avril would say, "What the hell?"