English football whipped into a frenzy in January when the actions of Leeds United manager Marcelo Bielsa stuck in the craw of Derby County and their boss Frank Lampard.
The iconic veteran coach's methods of preparation were called into question after a dubious training ground incident, which has since been dubbed 'spygate' in reports and on social media.
Bielsa has been defiant about the issue, but his honesty in the face of scrutiny has won him some begrudging admiration from detractors.
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But what exactly is it and why has it prompted so much fury?