To be caught red handed means you’ve been caught doing an illegal or shameful act.
One theory is that the phrase was born in the Northern island province of Ulster. The tale tells of a boat race in which the first person to touch the shore of Ulster would be crowned king. One challenger, determined to win at any cost, allegedly cut off his hand and heaved it to the shore. This hand, to this day, is prominently displayed on Ulster’s flag. Unfortunately, this red handed backstory is a myth.
Caught red handed actually originated far away from Ireland in a place called … Scotland. The Scots began using the phrase as far back as the 15th century. Now, Scotland at this time did not have fancy forensic scientists or crime scene investigators, and a proper police force was still decades away. So, it was up to the citizens of Scotland to fight crime, and they adopted a no-nonsense way of solving murders.
The Scots presumed that a person guilty of murder most likely had blood on his or her hands. So if anyone was seen with bloody hands, they were said to be caught red handed. The saying remained in Scotland for the next several hundred years. Until, in 1819, Sir Walter Scott popularized it in his novel Ivanhoe. As his novel gained popularity around the world, so did the phrase.