I will be copying a small paragraph at a time from the IBJJF rules website and hope to educate our readers on a informal way.   "When an athlete forces his/her opponent to the ground on all fours or belly-down, points shall only be awarded once the athlete performing the takedown has established a back clinch on his/her opponent—hooks need not be in place but at least one of the opponent’s knees must be maintained on the ground for 3 (three) seconds." http://ibjjf.org/rules/