Three arrests is hardly indicative of trouble though.
It really is a non shocker that fans who spend 90 minutes of a football match goading the opposition fans go and 'confront' those same fans when they get on the pitch! I imagine the presence of a couple of skates in there - one with a smoke bomb [allegedly], didn't do much to calm the situation!! Personally I would blame the stewards for that, as I distinctly remember attending an away match at Cardiff in the middle of winter and being stopped before entering the ground and asked to undo my coat to show what I was wearing underneath - presumably they were checking I was a Saints fan rather than a Swansea fan