Default Level a discipline is played at if not declared

Minion A is in combat with Minion B. Minion A is acting. Minion B plays Burst of Sunlight, and immediately plays Rotschreck, without declaring the discipline level of Burst of Sunlight.

This is not uncommon for players to do something like this as they assume it won't matter due to Rotschreck. However today this happened:

A third player then plays Sudden Reversal on the Rotschreck.

So what is the official ruling for the default discipline level of a card played if it is not declared?

I thought I saw an official ruling about this, maybe from back in the LSJ days, but I can't find anything now.

steveharris wrote:

So what is the official ruling for the default discipline level of a card played if it is not declared?

I thought I saw an official ruling about this, maybe from back in the LSJ days, but I can't find anything now.

You're probably remembering the ruling about things like Animalism retainers, which enter play at inferior if they come in through some method that doesn't go the 'normal' route.
For actual play of cards, if you haven't declared what the effect was, that's a mis-play. You have to make sure people know what you're doing with a card when you play it. Roll back and correct it. If (in the judge's opinion) someone is intentionally mis-playing cards to get information, penalise them appropriately in a tournament situation.