Stop a player moving while casting?

Hi . I was Wondering on how to stop a player moving while they are casting a spell i found this

function FireballImage::onCharge(%this, %obj, %slot)
{
%obj.client.player.maxForwardSpeed = 0;
%obj.client.player.maxBackwardWalkSpeed = 0;
}
So isthat right or because it has no effect in game