... and what he has on second report was fiddled! (10)

I believe the answer is:

sportswear

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'and what he has' is the definition.
The definition suggests a singular noun which matches the answer.

'second report was fiddled' is the wordplay.
'second' becomes 's' (common abbreviation).
'fiddled' indicates an anagram.
'report'+'was'='reportwas'
'reportwas' is an anagram of 'portswear'.
's'+'portswear'='SPORTSWEAR'

'on' acts as a link.

Can you help me to learn more?

(Other definitions for sportswear that I've seen before include "Clothing" , "Gear" , "Kit for games" , "in which triathletes swim" , "clothes for play" .)

I've seen this clue in The Telegraph.

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