Yarn that stretches? It might, say, in the middle (4)
I believe the answer is:
saga
'yarn that stretches?' is the definition.
'saga' can be an answer for 'yarn' (thesaurus). I'm not certain of the remainder of the definition.
'it might say in the middle' is the wordplay.
'it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
'might' becomes 'g' (I can't justify this - if you can you should give a lot more credence to this answer).
'in the middle' indicates the central letters.
The middle of 'say' is 'a'.
'sa'+'g'+'a'='SAGA'
Can you help me to learn more?
(Other definitions for saga that I've seen before include "Epic story" , "Soap opera" , "long series of events" , "Chronicle; adventure" , "Epic tale" .)