Foul number 51 in the team (7)

I believe the answer is:

squalid

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

'foul number' is the definition.
'squalid' can be an answer for 'foul' (both can mean disgusting). I am not sure about the 'number' bit.

'51 in the team' is the wordplay.
'51' becomes 'LI' (Roman numerals).
'in the' is an insertion indicator.
'team' becomes 'squad' (sports team).
'li' put within 'squad' is 'SQUALID'.

Can you help me to learn more?

(Other definitions for squalid that I've seen before include "Dirty, unpleasant" , "run down" , "Run-down - filthy" , "Seedy" , "Foul" .)

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

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