In short, the player would have a normal speed afterwards and after walking for awhile he will begin sprinting.
The sprinting would stop if the player clicks or stops moving/begins moving backwards (also this should not happen while moving backwards or strafing).
For instance, the player would walk 2 seconds constantly then after that he begins walking faster, without any stamina usage or any other supposed penalties.
Why would anyone want this? There is a sprint playertype already.
Except that this is not the same thing.
The sprint playertype requires you to right click. That can be a bad thing in certain situations, also can be used indefinitely. Additionally you could sprint whenever, here the reason for sprint is solely so you can walk long distances faster, not for being able to dodge anything, though it could also be used per se.
I think this is a really good take on sprinting since could be used in per-general basis. Perhaps different playertype variations could also determine how long it would take to walk in order to reach the sprinting stage.
This is basically the way the sprinting works in War of The Roses by the way.
