Free parking will be nigh on impossible. There are designated car parks along the 316.. Experience has shown, it is easier to drive up the 316, turn around at the roundabout closest to the rugby ground, and park in one of the grassy car parks. This way, your facing the right way down the 316 when you try and drive out.. If you do opt for the "free" parking on the side streets, be aware that after the match, the police will be enforcing a very strict one way system, and closing roads that normally make for easy access out of there..
Being rugby supporters, the car parks are quite civilised, with plenty of peeps quffing the champers and pimms whilst waiting to go and watch the match..