a whole new ballgame idiom
完全不同的情况，完全是另一回事儿（尤指难事或自己知之甚少的事情）
a completely different situation, often one that is difficult or that you know little about
We'd done a lot of climbing in Scotland but the Himalayas were a whole new ballgame. 我们之前在苏格兰登过不少山，但攀登喜马拉雅山则完全是另一回事儿。