Taylor Swift -- Bum-Rushed By Obsessed Fan ... Manhandled By Security

Scary moment for Taylor Swift ... when an obsessed fan blew past security and confronted her on stage at her concert in London ... while Taylor's bodyguards scrambled to save her.

It all went down at the O2 Arena ... when Taylor was performing her smash song, "We Are Never Ever Getting Back Together."

That's when a pretty sizable male fan charged the stage ... and got face-to-face with the singer.

Moments later, two male security guards sprinted to Taylor's side ... grabbed the stage intruder by the arms ... and ripped him off the stage.

Of course, Taylor continued the show like nothing ever happened.