I noticed this when I got on at Portslade, the Portsmouth service was absolutely rammed with Day Trippers it’s always a busy line on a Saturday so I can see that being a issue, I don’t think it helps that the West Worthing services have been cancelled as a Covid measure
For league games we're going to group up to make a four with my mate and his son who are our "bubble" anyway. He normally drives to Brighton and then we train from there. I think we'll have to stick to that. With 6-7000 crowds to start with it should be easy enough to distance a train queue. Falmer station was fine - we stayed in our seats till it was safe to leave, had a pint and then ended up on the same train back as the mates we'd accidentally bumped into (not literally!) on the way over. Very, very easy to distance.
I can imagine some of the London/Brighton trains are quite packed as well.