if you were going for a double leg takedown on the street it would probably work better if you dropped on one knee to do it but would also scrap up your knees on the street...what would you do in a street fight???go on your knees and do the takedown or just do it by ducking low.

I personally would try not take anyone to the ground unless had no choice. But that was not your ? I would strike first and enter in on my feet for the reason I wont scrape my knees but I think you can get away from a knee if they throw a knee you stand up and get away.