Extended, diffuse radio emission (halos and relics) in galaxy clusters is a rare phenomenon. The origin of these radio sources and their connection with cluster mergers is still being debated. Here we present the results of the DARC program, aimed to the internal Dynamics Analysis of ”Radio” Clusters and mainly based on a long-term TNG-INT program (20 clusters at z=0.1-0.3). The study of kinematics of member galaxies show that DARC clusters are examples of very substructured systems and allow us to detect and weight the interveining subclusters, as well as to obtain infor- mation about their relative motions and the merger geometry. The multiwavelength observational picture (optical, radio and X-ray) of DARC clusters is well interpreted in a scenario of a recent, major cluster merger.