I know at the snap of the ball a defensive back can make contact with the receiver if he is still within five yards of the LOS. Is there any rule saying all he can do is make brief contact or can he sustain contact as long as he is in that five yard window? With so many passes based on timing and the QB usually just having 4-5 seconds to get rid of the ball, I was wondering why defensive players don't just lock the receivers up and not let them release down the field. If they just did that for two seconds it would throw off every timing route and and typically just leave the QB a very small window to do something with the ball before the pass rush got to him.