Ground team splits up to bombard enemy lines? (4,4)
I believe the answer is:
hate mail
'bombard enemy lines?' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'ground team splits up' is the wordplay.
'ground' is an anagram indicator ('grind' the letters into a new form).
'splits' means one lot of letters goes inside another (some letters split a word into two).
'up' becomes 'hail' (I can't explain this - if you can you should give a lot more credence to this answer).
'team' with letters rearranged gives 'tema'.
'tema' inserted inside 'hail' is 'HATE MAIL'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for hate mail that I've seen before include "communication with animosity - with 19a" , "Offensive correspondence" , "Poison-pen letters" , "Abusive letter that expresses loathing" , "Nasty letters" .)