Auto-hitting is where you make your character literally strike another character without the other player's permission and/or without allowing a way for them to avoid it if they choose.

Auto-hit example: "Steve punched Shaun in the face."

Correct form: [u]"Steve swung his fist at Shaun's face."[/u]

The latter example allows the other player to either;

Take the hit: "Shaun stumbled back, clutching a bloody nose."

Or dodge: "Shaun ducked and Steve's punch passed harmlessly over his head."

Characters are usually allowed to fight each other, but the attacking character is never allowed to hit another character without the controlling player's permission. You can use phrases like "shot at", "tried to hit", "aimed for" and so on, which gives the defending player the option of whether or not they want to allow their character to be hit. Auto-hitting is ignoring that courtesy and inflicting damage without giving the defending character/player the option to evade it.