Sleeveless garment -- team's leader is after one (7)
I believe the answer is:
singlet
'sleeveless garment' is the definition.
(I've seen this before)
'team's leader is after one' is the wordplay.
'team's leader' becomes 't' (I can't justify this - if you can you should believe this answer much more).
'is after' means one lot of letters go next to another.
'one' becomes 'single' (similar in meaning).
't' put after 'single' is 'SINGLET'.
Can you help me to learn more?
(Other definitions for singlet that I've seen before include "top gear" , "Underwear" , "Sleeveless garment" , "Sleeveless shirt" , "Something to wear" .)