Skate and skate? Oh m-my, son will go sprawling! (8)
I believe the answer is:
homonyms
'skate and skate?' is the definition.
(the fish skate and the verb skate are an example)
'oh m-my son will go sprawling' is the wordplay.
'm-my' becomes 'mmy' ('my' said with a stammer like 'my' was).
'will go sprawling' indicates anagramming the letters.
'oh'+'mmy'+'son'='ohmmyson'
'ohmmyson' is an anagram of 'HOMONYMS'.
(Other definitions for homonyms that I've seen before include "Two words that have the same spelling but different meanings" , "Words which, though pronounced the same way, have different meanings" , "Words that sound the same, though with different meanings" , "Words that sound the same as others but have different meanings" .)