In The Witcher, Geralt should use the Fast style of fighting against these opponents, unless they are in groups of three or more, then Group style is recommended. If you find yourself unable to hit an opponent, it is probably because they are quicker than you are. How can this be you ask? No one is quicker than a witcher... It is because you are probably using the Strong style of fighting and your opponent is simply quicker because you are wasting energy winding up for a killer blow and he is not. Switch to Fast style — by using the X-key or clicking on the Fast style icon — and things will proceed much more smoothly.