They both move away from the central "average" phenotype

They both move away from the central "average" phenotype.

Directional selection is described as the selection for a particular extreme phenotype in the population as opposed to the other phenotypes. This causes a shift in the allele frequency in the population as more individuals have the favourable adaption due to the selection pressures.

Disruptive selection is when the population has selection pressures acted upon it that selects against the average phenotype and the extreme phenotypes are selected for. Over time a distinct difference can be seen in the population and the population might separate due to their extreme differences in that particular phenotype.

In both types of selections, the average phenotype is selected against and the extreme phenotypes are selected for.