Grab a suitcase from an overhead rack and hold it in front of you while running towards him. No need to run straight into the knife (thought the perp was so intent on stabbing his randomly chosen victim, that it’s not clear he’d have bothered to turn around if someone had been coming at him). And actually, a couple of people throwing suitcases and duffle bags at the guy should have been able to get him down on the ground.
I hadn’t thought about suitcases being in an overhead rack. Do they do that on buses? I’ve always pictured the luggage in the undercarriage bins. I’ve never taken a trip on a commercial bus line before.