The former One Direction singer was in San Antonio Friday night with his Instagram model GF, Maya Henry -- who's reportedly only 19 years old. As you can see in this video, things got a little feisty when they ended up at a bar called the Silver Fox.

Witnesses tell us Liam and Maya were able to get in at first -- having been recognized by others -- but later came this dust-up with security. In this clip, you see Liam -- who's wearing a white shirt with a bunch of dirt on his back -- trying to come face-to-face with a bouncer, or possibly several. He's being held back, and at one point you hear him say, "Don't f***ing push me again. I swear to God I'll lay your ass out."

Witnesses tell us Liam was, in fact, pushed to the ground -- hence the dirt on his back -- after he and Maya left and tried to reenter the bar. We're told security stopped them because of Maya's age, and when Liam tried forcing his way in ... he allegedly got shoved to the ground and followed up with this.

Eventually, we're told Liam and co. decided to leave on their own. Police were not called.

He took to Instagram to claim he'd been "jumped" by three of the bouncers there, tagging the establishment and threatening to take them to court. He's since deleted that post.

BTW, Maya's from the San Antonio area, so it looks like Liam was in town celebrating Thanksgiving with her.

We've reached out to both parties, including Liam's team ... so far, no word back.

Fun fact: Maya's family is kind of a big deal in San Antonio. Her dad is personal injury attorney Thomas J. Henry, who hired Pitbull and Nick Jonas to perform at Maya's quinceanera!!