Spontaneous umpire attended sports (14)

I believe the answer is:

unpremeditated

'spontaneous' is the definition.
(thesaurus)

'umpire attended sports' is the wordplay.
'sports' indicates an anagram (I've seen 'sporting' mean this).
'umpire'+'attended'='umpireattended'
'umpireattended' is an anagram of 'UNPREMEDITATED'.

I've seen this clue in The Independent.

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