Ruslan, bhopping is possible due to the terrible physics employed by Valve...lol. On most mod servers the gravity is up and the airaccel is high. If you time it right when you jump, and then hop, you can pick up speed because the server thinks your "falling" but you also have forwards momentum. Once you can do it on the mod servers, doing it in Dust2 becomes slightly easier - And all the more fun because it makes people RAGE. The eGO servers are set up to disallow it though, but a few of the dodgier ones have bhopping. Its also great for nearly every mod - GG, DR, ZM, Pb, bhopping on these gives you massive advantages. If you want to know how, YouTube how to bhop and find a bhop server - bhop_advi, bhop_aoki, bhop_snowhite and bhop_wood are alright to learn on, snowhite being the easiest map invented and advi and aoki being the longest.