Impressive archer getting middle of rings (7)
I believe the answer is:
telling
'impressive' is the definition.
(I know that impressive can be written as telling)
'archer getting middle of rings' is the wordplay.
'archer' becomes 'tell' (folk hero William Tell).
'getting' means one lot of letters go next to another.
'middle of' indicates the central letters.
The middle letters of 'rings' are 'ing'.
'tell'+'ing'='TELLING'
(Other definitions for telling that I've seen before include "Revealing, significant" , "Powerful - effective" , "Powerful; relating" , "of significance" , "Counting" .)