Pitcher knew error was in the midfield (4)

I believe the answer is:

ewer

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

'pitcher' is the definition.
(I know that pitcher can be written as ewer)

'knew error was in the midfield' is the wordplay.
'EWER' is hidden in amongst the letters.
However, I am unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for ewer that I've seen before include "Were (anag)" , "29 [VESSEL]" , "Jar for water" , "Container" , "A wide-lipped jug" .)

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

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