I don't think that's quite true. My first real encounter with football hooliganism came at the end of 69/70 season when we beat the jacks 2-0 in Welsh Cup Semi Final Replay at the Vetch. I was fourteen at the time and went to the game with a gang of schoolmates. As soon as we got off the bus and walked into the town centre, there were a gang of Swansea fans waiting for any City fans who had just arrived and all hell broke loose. Our gang scattered to the four winds and I ended watching the game with two others out of the original ten or so who traveled. We only met up again at the bus station after the game and although none of us were involved in the fighting, it turned out that we had all seen a lot of it as it went on for a long time before the match.
I remember that all of us were taken aback by the fighting because none of us had been expecting it, so we were not aware of any ill feeling beforehand, but it was definitely there and the way the jacks were waiting for us must have been pre planned.