It has been said earlier that the rocking from side to side visible in many sprinters during the first steps happen because of their acute departure-angle. Some people however seem to be doing this more than others regardless of any difference in departure-angle. Is this just a result of different builds or is there a technical side to this also?
Bailey and Aliu, who both have relatively long legs and a short torso, are examples of this more pronounced rocking from side to side.
I know that Angela Williams 4 time NCAA Champion rocks from side to side when she runs.
I did some biomechanics analysis on Kim Collins and I came to the conclusion that he rocks because he has a lot of upper arm thrust
on his vertical lift which causes him to rock side to side.
Throw your arms hard rapidly and you’ll see your body rock.
I feel Angela Williams rocks because of bad habit.
If she focus on her arm swing it’ll change in time.
It’s better now than her USC days.
But she also ran faster with this rocking.
You have a point there.
Who said rocking is bad you never know.
Rocking could be the best way to sprint 
In sprinting you just never know.
Maybe I should try to rock a little.
Sprinting is so tricky at times.
That is what I have experienced too. Recently I have focused on a more violent arm-drive at the start and besides improved acceleration this rocking from side to side has been the result.