汉语“抓个现行、当场抓住”的英语可用catch somebody in the act of doing，如
【例句1】He was caught in the act of stealing a car. （他偷车时被当场抓住。） [牛津高级学者辞典]
【例句2】The gang was caught in the act of unloading the cigarettes. （那帮人在卸烟时被现场抓住了。）[朗文当代英语词典]
【例句3】It is often difficult to tell when someone is using drugs unless they are caught in the act. （除非被当场抓获，否则通常很难判断某人何时吸毒。）[牛津高级学者辞典]
对“抓个现行”，英语还有个形容词red-handed。
成语“捉奸捉双”和“捉贼捉赃”，并非真的去捉奸和捉贼，而是要有铁证。对于凶杀案，若嫌疑人手上有血，那么在古代英国司法中肯定是重要证据，这就是red-handed的语义逻辑，如
【例句4】He was caught red-handed (=as he was doing something wrong) taking money from the cash register. (他从收银机里偷钱被当场抓住。)[朗文当代英语词典]
【例句5】Earl was caught red-handed taking the money. (厄尔偷钱当场被抓。)[朗文当代英语词典]
【例句6】My boyfriend and I robbed a store and were caught red-handed. (我和男朋友抢劫了一家商店，当场被抓。)[柯林斯高级学者辞典]
上述red-handed被标为形容词，但它更像修饰catch的副词。尤其是对【例句4和5】，形容词修饰动名词，尤其是带宾语的动名词，比较少见，这是因为动名词在短语内部是动词。
red-handed最初与凶杀案关联，但就像汉语的“捉奸捉双”一样也被泛义拓展了。不过，肯定不能用于褒义语境。
in the act of doing something没有贬义，它就是“在做某事的行动中”，也就是“正在做某事”，如
【例句7】Ken was in the act of paying his bill when Neil came up behind him. （肯正在付账，尼尔走到他身后。） [柯林斯高级学者辞典]
【例句8】Lindsay paused in the act of putting down the phone. （林赛放下电话时停顿了一下。）[朗文当代英语词典]
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