Martial arts insiders took a RAT everywhere (6)

I believe the answer is:

karate

I'm a little stuck... Click here to teach me more about this clue!

'martial arts' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'insiders took a rat everywhere' is the wordplay.
'KARATE' is hidden in amongst the letters.
But, I am unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for karate that I've seen before include "Japanese martial art" , "Japanese art of unarmed combat" , "fighting system" , "A taker (anag)" , "A Jap. martial art" .)

I've seen this clue in the Sydney Morning Herald.

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