Worker with horses less happy about foal’s backside (7)
I believe the answer is:
saddler
'worker with horses' is the definition.
I can't judge whether this defines the answer.
'less happy about foal's backside' is the wordplay.
'less happy' becomes 'sadder' ('sad' can be the opposite of 'happy' so perhaps 'sadder' is reasonable for 'less happy').
'about' is an insertion indicator.
'backside' indicates one should take the final letters (the letter at the back).
The final letter of 'foal' is 'l'.
'sadder' going around 'l' is 'SADDLER'.
Can you help me to learn more?
(Other definitions for saddler that I've seen before include "he'll offer you a seat" , "Leather-worker" , "Maker of horse's equipment" , "One makes leather goods for horses" , "Maker of seats for riders" .)