One sort of mate (4)
I believe the answer is:
'one sort' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'of mate' is the wordplay.
'of' indicates anagramming the letters (the answer comes from or \'of\' the letters).
'mate' anagrammed gives 'TEAM'.
Can you help me to learn more?
(Other definitions for team that I've seen before include "A cooperative unit" , "Group or squad" , "Company" , "Competitive side" , "Mate for a group of players" .)