Tackle crack soldiers sent amongst leaderless group (9)
I believe the answer is:
equipment
'tackle' is the definition.
(tackle can mean equipment or gear)
'crack soldiers sent amongst leaderless group' is the wordplay.
'crack' becomes 'quip' (both can mean a joke).
'soldiers' becomes 'men' (men can mean a group of soldiers).
'sent amongst' means one lot of letters goes inside another.
'leaderless' means to remove the first letter.
'group' becomes 'set' (both can mean a collection).
'quip'+'men'='quipmen'
'set' with its initial letter removed is 'et'.
'quipmen' going within 'et' is 'EQUIPMENT'.
(Other definitions for equipment that I've seen before include "Apparatus, gear" , "outfit" , "Kit, apparatus" , "Items needed for a particular purpose" , "Stuff" .)