It is the most ethnically diverse city in the UK and it has seen a spike in Covid cases of late. Those things mean that it could be forced to stay in the current lockdown for at least the next two weeks. It would be the first local lockdown of its size in the UK if that was to happen - a bit of an experiment.
You have to feel sorry for the residents, but if you were a planner looking for somewhere to exercise and test such a thing Leicester would probably be near the top of your list. It sits on its own well away from other urban areas. Most of its people live within a well defined ring-road, It has no airport of note, and it is not a main rail hub.
I can understand the city's mayor, Sir Peter Soulsby, being angry, but there was always going to be a first. Hopefully it will be monitored carefully and with plenty of updates being given to businesses and the community. It will be easier to keep tabs on there than if it had been in one of those areas where cities bump up against one another such as W. Midlands, Greater Manchester or W. Yorkshire.