Britney Spears 'In Shock,' Angry After Slap as She Had Dinner at Catch in Vegas

Britney Spears was extremely agitated after getting slapped by a security guard protecting NBA phenom Victor Wembanyama ... according to an eyewitness and photos obtained by TMZ.

TMZ broke the story ... Britney was outside Catch restaurant at the Aria Hotel Wednesday night when she saw Victor and made her way to him for a selfie. She says she tapped him on the back -- he says she grabbed him -- and Victor's security guy backhanded her across the face. Metro police are now conducting a criminal battery investigation.

An eyewitness who was dining at Catch when Britney walked in tells TMZ ... as she walked in she said in a "very animated voice" that the security guard "punched" her in the face, as she pointed at the guy who was sitting at another table.

The eyewitness says Britney's security guy went over to Victor's security and asked the guy to come over to her table and apologize. The eyewitness says the guy walked over and said "I'm sorry," and said something to the effect he didn't know it was her when he made contact.

Britney seemed in shock, according to the eyewitness, and angry. She said she couldn't believe it happened and beelined it for the bathroom.

We've learned so far ... neither Victor nor anyone else from the San Antonio Spurs has reached out to Britney, and she is not pleased.

We covered it all in the latest episode of The TMZ Podcast, available on all podcast platforms.