Light, humorous piece of theatre almost at capacity (7)
I believe the answer is:
playful
'light humorous' is the definition.
'playful' can be an answer for 'humorous' (thesaurus). I am not certain of the 'light' bit.
'piece of theatre almost at capacity' is the wordplay.
'piece of theatre' becomes 'play' (I can't justify this - if you can you should give a lot more credence to this answer).
'almost' means to remove the last letter (most of the word but not all of it).
'at capacity' becomes 'full' (I've seen this in another clue).
'full' with its final letter taken away is 'ful'.
'play'+'ful'='PLAYFUL'
Can you help me to learn more?
(Other definitions for playful that I've seen before include "Fond of games; light-hearted" , "Lively" , "Frisky" , "Fun-loving" , "Frolicsome" .)