Terrorise legless reveller (9)

I believe the answer is:

roisterer

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'reveller' is the definition.
(I know that roisterer is a type of reveller)

'terrorise legless' is the wordplay.
'terrorise' can be anagrammed to 'ROISTERER'.
However, I'm not clear how this is indicated.

Can you help me to learn more?

(Other definitions for roisterer that I've seen before include "noisy party animal" , "Noisy reveller" , "Living it up" , "He's pushing the boat out" , "Noisy merrymaker" .)

I've seen this clue in The Telegraph.

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