"Dark Arts"

He doesn't give context to the comment but it seems an odd comment to make. You can get GPS jammers which will block GPS signals in a fairly small area. They are pretty popular things to put in cars amongst the crazy 'The government is tracking my every move' crowd in the US despite being highly illegal. And they are also illegal here as there is just way too much chance of either intentional or unintentional abuse (especially as they also interfere with Air traffic control so can turn an airport dark)

Other than that though I'm not sure what they could have done to stop City using them. It's only tracking Citys own players so the only people who could complain is the players (There are some Premier League players who have refused to waer them without having extra payments for the data collected to be paid as part of their contracts) and I'm not sure at League 2 level but at PL level they only really use them in pre and post match (or matches in pre-season). PL clubs for their ingame analytics are using Real time player tracking via camera's, the same system they used for offisdes in the world cup as its better for instant data that can impact the match rather than GPS which really only helps in post-match debriefs. Although you need cameras installed in the right location for this so you only get this benefit at home