te no hira o kaesu
to flip one’s palm
to change one’s tune after something unexpected has happened
It’s often used when one suddenly and completely changes his/her opinion about someone after they achieve something good or bad.
Until yesterday, a lot of people had been criticising the head coach, saying, “He is sh*t”. But once his team won the important match, they changed their tune and commended him, saying “He is a genius!”