catch someone red-handed
US /kætʃ ˈsʌm.wʌn ˌredˈhæn.dɪd/
UK /kætʃ ˈsʌm.wʌn ˌredˈhæn.dɪd/

1.
当场抓住, 抓个正着
to discover someone in the act of doing something wrong or illegal
:
•
The police caught the thief red-handed as he was trying to break into the car.
警察当场抓住了小偷,当时他正试图闯入汽车。
•
My mom caught me red-handed eating cookies before dinner.
我妈妈当场抓住了我,当时我正在晚饭前吃饼干。