Social danger of an encroachment is one of the characteristics going alongside with the concept of necessary defense. The question whether the encroachment must be not only socially dangerous but also criminal is still discussed in the theory of criminal law. The article supports the point of view that an encroachment must be objectively socially dangerous. It makes the defense possible even if the criminal is irresponsible or juvenile. The article also dwells on the problems whether necessary defense could be possible against the actions committed under the circumstances excluding unlawfulness and guilt of the action (the extreme necessity and others).