This issue is certainly not worth of a forfeit....even if it is one to be declared later. I'm going to work with the coach to try to find a way to avoid that. Even the other coach, in most cases, does't want a win that way.
I may offer him some options to resolve the situation....such as a timeout. Coach, "Did you just say you wanted a timeout?"
That player just might have his jersey untucked.....for that matter, the player could pull it out so he will be sent out.