Casey Affleck Takes an L at TSA Trying to Bring Baseball Bat on Plane

Casey Affleck must have forgotten he was at an airport and not home plate -- 'cause he casually tried bringing a baseball bat onto a plane.

We got Casey Thursday at LAX rushing to catch a flight, with bag and bat in hand ... and a ton of confidence he'd get through TSA.

When we ask if he really thinks he'd get past with the equipment, he says we'll see ... and see we did.

After what looks like several earnest attempts to persuade, Casey gets a definitive answer with one head movement.

Casey could have checked the bat, but decided to surrender it, and scurried to his plane.