The distributions of the recoil vector fluxes are studied using the binary collision lattice simulation code COSIPO in order to investigate the development of collision-cascade anisotropies in single-crystalline Cu. The vector fluxes are directly related to the angular distributions of sputtered particles. A single-crystal Cu(100) surface is used as the target, and is bombarded with normally incident 5-keV Ar ions. The results are discussed within the framework of focusing. The collision cascades are dominated by focusing along the (110) directions. Anisotropies in collision cascades turned out to be dependent on the interaction potential. The anisotropy in simulated angular distributions of sputtered particles is directly related to anisotropies in collision cascades.