Spots Henman finally breaking serve (4)
I believe the answer is:
acne
'spots' is the definition.
(skin condition causing spots)
'henman finally breaking serve' is the wordplay.
'finally' says to take the final letters.
'breaking' indicates putting letters inside.
'serve' becomes 'ace' (type of tennis serve).
The final letter of 'henman' is 'n'.
'n' put into 'ace' is 'ACNE'.
(Other definitions for acne that I've seen before include "Skin disorder" , "Skin affliction" , "Skin spots" , "Adolescent spots" , "Face problems" .)