Spoilsports! Initially one stops Charles doing what he likes (6)
I believe the answer is:
skiing
'doing what he likes' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'spoilsports initially one stops charles' is the wordplay.
'initially' says to take the initial letters.
'one' becomes 'i' (Roman numeral).
'stops' indicates putting letters inside (stopping can mean blocking a gap).
'charles' becomes 'king' (Charles I or Charles II).
The initial letter of 'spoilsports' is 's'.
'i' placed inside 'king' is 'kiing'.
's'+'kiing'='SKIING'
Can you help me to learn more?
(Other definitions for skiing that I've seen before include "going downhill fast" , "Mountain sport" , "Winter sports" , "Gliding over snow" , "Participating in a winter sport" .)