If you have larger pigs through late autumn and winter then the ground could get quite churned up. If it gets muddy to the point their bellies get muddy as they come out to feed or toilet, you must find somewhere else for them to be. (We all go through this and discover that free range pigs are very happy in spring and summer, and in winter, indoor pigs / pigs with shelter and a cement run, with lots of space and lots of straw - and lots of interesting things going on and people visiting them - are also very happy pigs!
If you can rest the ground after one batch of porkers, at the end of the summer, to let the grass regrow, and then get the next batch in winter, so that it's only smaller pigs on the ground when it's most likely to get muddy, you might get away with it. But if you are planning on having pigs through the winter, make sure you have indoor accommodation you can move them to if you need to.