I think if I was driving and saw JJ arms, or who ever was starting them, start to move I would make my move
The OKC boys video the starting line and don't like you to do that so EXACT details on what makes a jump would need to be discuss before racing

There is no "jump" by Memphis rules. Chase is a race. If one guy jumps and you chase the race is on. If your oponent jumps and you don't move, then he would loose. Think about it. We all leave .4-.5 before the green light. These guys are leaving before the arm drop for sure. But the have it down to a science. The car isn't moving until the arms drop. But the drivers process has started well before that time.
Doug

I have seen on the show where one of the racers did move before his arms went up and the other racer didn't move so that racer won by the other car jumping
When we would race on the streets in SO CA we would, the out of town racers, we would make sure that the starters arms had to be starting down before we could "jump". The starters would point to each car and look for the head nod or thumbs up and once they saw that they would raise their arms above their shoulders and then drop them. If you started to move before the arms where coming down you jumped. I was accuse more than once of jumping but when I explained I saw his arms start down and then hit the throttle instead of waiting for his arms to be pointed straight down before gassing it I usually won the arguments
Some times I would wait until I saw the other car start to move before flooring it when I knew I could beat them badly
That tactic would sometimes allow me to milk that cow twice or more

Test test test. I did. Thought I had a great street tune. It didn't work on there road. The road we were on was no where near the road I tested on or the road I raced them on last time. The new road sux even with rubber on it. Cars that always dead hook blew the tires off.