Buster Posey fired Giants manager Bob Melvin:

“After careful evaluation, we determined that making a change in leadership was in the best interest of the team,” said Buster Posey, the Giants’ president of baseball operations. “The last couple of months have been both disappointing and frustrating for all of us, and we did not perform up to our standards. We now turn our focus to identifying a new leader to guide us forward.”

…

“It’s definitely not ideal but unfortunately we talked about it a lot what the standards are for the Giants and we have high standards,” Posey added. “And I hold myself to those same standards. I understand fully the position that I’m in now. My job and the team”s success is evaluated accordingly as well. You without a doubt hope that there can be consistency in these leadership positions. We’ve got to get back to a place where we’re getting in the playoffs, we’re making runs in playoffs. That’s what our fan base deserves, that’s what the city deserves.”

ESPN.com

This strikes me as more house cleaning than Melvin doing a poor job. Sometimes bosses want people they like working under them, and Posey obviously wants someone else.