if you shift your ground in an argument or a discussion, you start to express a different opinion.
He's impossible to argue with because he keeps shifting his ground.
shift (one's) ground
To adopt a different viewpoint or opinion. I was shocked when Liz suddenly shifted her ground and started seeing things as I did.
shift your ground
say or write something that contradicts something you have previously written or said.
shift your ˈground
(usually disapproving) change your opinion or position, especially during an argument or a discussion: He’s shifted his ground on many major policy issues. OPPOSITE: stand fast/firm