What's the difference between a brat and a submissive?

A brat is a submissive who resists on purpose, because being caught is more fun than going along with it. The resistance is the play.

The distinction that matters is between bratting and topping from the bottom. Bratting is a game both people agreed to, with a clear stop signal. Topping from the bottom is quietly taking control you didn't negotiate for, and it usually means something wasn't discussed properly.

If you're not sure which one is happening, that's the conversation to have before the next scene rather than during it.