I did some martial arts ad self-defence training for several years, and we ran scenarios for two-three people attack on one of us. The main thing was to use a lot of groin kicks, elbow punches etc. - anything that can inflict quick damage and incapacitate as many attackers as possible. It is interesting how quickly people will stop from attacking you if they sense that you know what you are doing. However, if there is a knife involved then we were told that the best solution would be to run away (if you can). It is not worth it confronting someone with a knife, unless you are very skilled in self-defence. Shielding yourself with one of the attackers is not actually that easy, as it will slow you down and also limit your filed of vision.