Jamie Lynn Spears — Pulls Huge Knife on Crowd to Break Up a Fight

EXCLUSIVE

Britney Spears‘ kid sister is a sandwich shop vigilante … who didn’t hesitate to reach for the closest stick when her girlfriend got into a brawl with another chick.

The violence broke out last weekend at the Pita Pit in Hammond, Louisiana — Jamie Lynn Spears and a friend had made a late night stop for food, when … according to sources accurate to Jamie … someone attacked her friend.

Cops tell us Jamie’s friend got clocked with a pot. That’s when Jamie went all “Saving Private Ryan” … dragging her friend to safety. Our Spears sources say Jamie pulled her behind the sandwich counter — then grabbed a long serrated bread knife and started waving it around to stop the fight.

We’re told that did the job. Police showed up, but Jamie’s friend didn’t want to press charges … so no one got arrested.

Hours before springing into action — Jamie posted a pic looking cool and demure.

It’s always the silent ones.