Colleagues forming teams (5)
I believe the answer is:
mates
'colleagues' is the definition.
(I've seen this in another clue)
'forming teams' is the wordplay.
'forming' indicates anagramming the letters.
'teams' anagrammed gives 'MATES'.
(Other definitions for mates that I've seen before include "Friends among the ship's officers" , "Pals or spouses" , "Pals, pairs" , "Chums" , "conclusive moves on board" .)