Why Solange Knowles attacked Jay Z [VIDEO]

Why Solange Knowles attacked Jay Z [VIDEO], Jay Z was attacked by Beyonce's sister Solange Knowles as the trio -- and a body guard -- rode in an elevator during a May 5 Met Gala after party.

Published surveillance video from the moment by TMZ hilights Solange kicking and swinging at her sister's husband after she joins Jay Z and Beyonce in an elevator. Solange is soon held by Jay Z's security guard after the attack, but she continues to thrash at the rapper. Go here for more including photos and video.