This is a repost from the SoTG which garnered a decent amount of support, but never got acted upon:
OK, the actual Chance Substitution rules have apparently been completely ignored in reffings for quite a while (A large portion of people have only found this out through an IRC debate today). I'm actually gonna post a suggestion to add to the Data Audit thread in lieu of the current rules, and use the popular method:
"Chance Substitution: A substitution based upon an event where it is uncertain that the event will occur. They can either change the action during which the event occurred, or an action after the event.
If used during the action during which an event occurs, the event must occur before the action. In addition, the Priority of the substitution action must be the same as the priority of the action that is now being replaced. If a move has multiple stages, the first priority stage is used."
This enables subbing for paralysis occurring or burns occurring in the action which a response is wanted - which is actually illegal.