The legality of owning a majority share in two football teams within the same league depends on the regulations of the governing bodies overseeing the competition. UEFA, for example, has strict rules against multi-club ownership when it comes to European competitions like the Champions League, to prevent conflicts of interest and maintain sporting integrity.
In some domestic leagues, ownership of multiple clubs is restricted or outright banned, while others may allow it under certain conditions. For instance, Italy has enforced rules preventing owners from controlling multiple clubs in the same division. However, in leagues like Saudi Arabia, the Public Investment Fund (PIF) holds majority stakes in multiple teams, such as Al Nassr, Al Ahli, and Al Hilal