Not against this in principle, but have issues with the detail. Prof Jason Leitch said a few days ago that he had no problem with crowds at large events, outdoors or even indoors. His issue was with how people were going to get there ie in crowded buses or trains. Now given that public transport will be minimal on Boxing Day, couldn't the restrictions have come into force on the 27th? Maybe not a huge issue you might think but many clubs will be detrimentally affected by that one day's change.
In any event, many people are totally disregarding basic laws and advice, like the wearing of face coverings, anyway but thats a wider public health enforcement issue.
As an aside, many clubs will find it difficult to ballot season ticket holders in time for Sunday.