Press Release issued by the NO2 Limits Expedition, 28 April 2013. Simone Moro has subsequently said in an interview that the expedition is abandoning its attempt on Everest.
At about 8am on 27th April 2013 Simone Moro (IT), Ueli Steck (CH), and Jonathan Griffith (UK) left Camp 2 to reach a tent at around 7200m (lower Camp 3) on the Lhotse Face of Mount Everest. A team of high altitude sherpas were 'fixing' the Lhotse face and the climbers were asked to not touch the fixed ropes they were establishing. As such the trio climbed about 50m away and to the side of the Sherpa team to avoid disturbing them in their work. It should be noted that all three climbers have extensive climbing experience all over the world and were very aware of the work being carried out by the Sherpas and the respect given to them for it.
...By the time the climbers descended back to Camp 2 some 100 Sherpas had grouped together and attacked the three climbers. They became instantly aggressive and not only punched and kicked the climbers, but threw many rocks as well.
Follow the link at the end of the article for a "sherpa point of view," provided by Garrett Madison, expedition leader for Alpine Ascents.