Sadly upset about an early start, shows no haste (6)
I believe the answer is:
delays
'shows no haste' is the definition.
Although both the answer and definition are verbs in their -s form, I cannot understand how they can define each other.
'sadly upset about an early start' is the wordplay.
'upset' is an anagram indicator.
'about' indicates putting letters inside.
'start' suggests taking the first letters.
The first letter of 'early' is 'e'.
'sadly' anagrammed gives 'dlays'.
'dlays' going around 'e' is 'DELAYS'.
Can you help me to learn more?
(Other definitions for delays that I've seen before include "Holdups, postponements" , "Hold-ups or deferrals" , "From waits" , "Holds back, causes to be late (6)" , "Postpones or holds back" .)