Young people seen playing after end of August (5)
I believe the answer is:
teens
'young people' is the definition.
(I've seen this in another clue)
'seen playing after end of august' is the wordplay.
'playing' indicates an anagram.
'after' means one lot of letters go next to another.
'end of' says to take the final letters.
The last letter of 'august' is 't'.
'seen' is an anagram of 'eens'.
'eens' after 't' is 'TEENS'.
(Other definitions for teens that I've seen before include "seven-year period" , "Between 12 and 20" , "children" , "Years 13-19" , "Adolescence" .)