#6 Massimiliano Allegri and Leonardo Bonucci

It all started with substitutions. Mario Lemina (now a Southampton player) replaced the injured Sami Khedira in the 46th minute and Stefano Sturaro left the field for Juan Cuadrado with 20 minutes left of regular time.
However, the substitution of Claudio Marchisio for Tomás Rincón was the proverbial straw that broke the camel’s back because it ignited animosity between a subordinate and his master.
Despite being three-nil up, Bonucci questioned Allegri’s decision to substitute players, something which is entirely at the discretion of the manager. Moreover, since no top manager tolerates insubordination (Beckham caught a boot to his face when he disrespected Sir Alex Ferguson), Allegri berated Bonucci (including calling him ‘d*ckhead” and even telling him to 'f*ck off)'.
Afterwards, Allegri threatened to resign unless Juventus suspends Bonucci. The club acquiesced to Allegri’s demands and duly suspended Bonucci and also forced him to apologise to Allegri in front of the entire squad.
This whole development strained the Juventus-Bonucci-Allegri relationship triangle. Thus, Bonucci ditched the dominant Juventus for a promising (or, in hindsight, not so tantalising) project in Milan.