Southampton broke the following EFL regulations (note: #127 was brought in specifically following the previous Leeds United / Marcelo Bielsa spying debacle).
EFL Regulation 3.4: the duty for clubs to act towards each other with ‘utmost good faith’.
EFL Regulation 127: the rule that prohibits a club from observing, or attempting to observe, another club’s training session within 72 hours of a scheduled match between the two clubs.