Groups causing a stir, strangely, about nothing (5)
I believe the answer is:
trios
'groups' is the definition.
The answer is an example.
'stir strangely about nothing' is the wordplay.
'strangely' is an anagram indicator.
'about' indicates putting letters inside.
'nothing' becomes 'O' (looks like zero - 0).
'stir' with letters rearranged gives 'tris'.
'tris' placed around 'o' is 'TRIOS'.
'causing a' is the link.
(Other definitions for trios that I've seen before include "Works for three players" , "Groups of three" .)