Blend in with the teeming legion (6)
I believe the answer is:
mingle
'blend' is the definition.
(I know that blend is a more specific form of the action mingle)
'in with the teeming legion' is the wordplay.
'in' indicates the answer is hidden within the clue.
'MINGLE' is hidden within 'with teeming legion'.
(Other definitions for mingle that I've seen before include "Mix, get involved with people" , "Blend" , "Dawn song, poem" , "Join the crowd, mix in" , "Circulate, socialise" .)