It all went down around 1:30 PM PST -- right before the stars began to arrive.
Law enforcement sources tell TMZ they believe a 28-year-old dude scaled a six or seven foot fence, got on to the red carpet and began "skipping."
We're told he then broke in to a run but cops immediately caught up with him and escorted the dude to the ground.
The man was arrested for trespassing. He's currently being held on $5,000 bail.