This is also basically what happened right at the beginning when the rioters very violently broke through the first fence badly injuring at least one cop. As so

This is also basically what happened right at the beginning when the rioters very violently broke through the first fence badly injuring at least one cop. As soon as it was obvious the mob was overwhelming things and the police had rescued their colleagues they fell back at a run to the next line. Pretty standard defensive tactics from time immemorial. That there were only three officers and a fence that was easy for the rioters to lift and batter the police with is concerning.