It’s silly to be spiteful to a slow starter (6)
I believe the answer is:
scatty
'it's silly to' is the definition.
I can't judge whether this definition defines the answer.
'spiteful to a slow starter' is the wordplay.
'spiteful' becomes 'catty' (I've seen this before).
'to' says to put letters next to each other (I've seen this in other clues).
'starter' indicates taking the first letters.
The initial letter of 'slow' is 's'.
'catty' put after 's' is 'SCATTY'.
'be' is the link.
Can you help me to learn more?
(Other definitions for scatty that I've seen before include "Slightly crazy" , "Not thinking straight" , "Informally crazy or feather-headed" , "Informally silly or crazy" , "Feather-brained" .)