Bedard had some more information on this on Boston Sports Journal.
It's been building up for awhile.
Guerrero has become more and more intrusive as he's started treating more players.
He's treating around 20 players now, and ordering them not to follow the training staff orders if he disagrees with them. For example, one player was supposed to do squats and Guerrero ordered him not to. This has pissed off the training/medical staff.
BB tried to speak to him about having everybody on the team on the same page, and Guerrero gave a different account that put Bellichick in a very bad light.
Some people at Gillette are referring to 'Yoko Guerrero'.