After end of play stage will be left so dull? (13)
I believe the answer is:
characterless
'dull?' is the definition.
(I've seen this before)
'after end of play stage will be left' is the wordplay.
I cannot really understand how this works, but
'play' could be 'act' (synonyms) and 'act' is found within the answer.
'be' could be 'are' (I've seen this in another clue) and 'are' is located in the remaining letters.
'left' could be 'l' (common abbreviation) and 'l' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'so' acts as a link.
Can you help me to learn more?
(Other definitions for characterless that I've seen before include "Lacking a distinctive nature" , "Dull" , "Lacking distinctive qualities" , "Nondescript" .)