Again, f(x) has stirred up some controversy related to behavior and mannerisms.  

This time, attention is focused on Sulli, who was clutching the hem of her skirt instead of dancing to 'Rum Pum Pum Pum' during f(x)'s performance on September 11.  The girls were on stage for the World Federation of Neurosurgical Societies symposium, which was taking place in Coex this year. 

Netizens are pointing out that she failed to do the part of the dance where the girls lie on the ground and eventually push themselves back up to the music.  In the pictures above, Sulli is just squatting down while holding her skirt.  People are saying she is not trying her best and leaving criticism on YouTube and on-line forums.

One criticism said, "She has neither the energy nor the drive.  Far from giving fun and energy to the audience, it feels like she is taking them away."  Another said, "Maybe Sulli really is not meant for the idol life as she doesn't seem like a pro the way she always surprises people with her attitude."

However, others have defended her, saying it might be due to her sudden diet plan or perhaps the skirt was too short and she just felt embarrassed.

SM Entertainment spoke up in her defense, as well, saying, "It appears that Sulli failed to follow the choreography because she was not feeling well at the time."

The part occurs at 1:20 in the video below. Check it out and let us know what you think.