A scruff grabbing a good person’s foot (8)
I believe the answer is:
anapaest
'foot' is the definition.
(type of metrical foot in poetry)
'a scruff grabbing a good person's' is the wordplay.
'scruff' becomes 'nape' (synonyms).
'grabbing' means one lot of letters goes inside another.
'good person' becomes 'st' (saint).
'nape' enclosing 'a' is 'napae'.
'a'+'napae'+'st'='ANAPAEST'
(Other definitions for anapaest that I've seen before include "part of a line of verse" , "Metrical foot with two syllables followed by one stressed syllable - try a peasant" , "involved in the destruction of Sennacherib?" .)