Urchins having sport, largely, in itinerant funfairs (11)
I believe the answer is:
ragamuffins
'urchins' is the definition.
(I know this)
'sport largely in itinerant funfairs' is the wordplay.
'sport' becomes 'game' (I've seen this before).
'largely' means to remove the last letter (most but not all of the letters).
'in' means one lot of letters goes inside another.
'itinerant' indicates an anagram (I've seen this in other clues).
'game' with its last letter removed is 'gam'.
'funfairs' anagrammed gives 'rauffins'.
'gam' placed within 'rauffins' is 'RAGAMUFFINS'.
'having' is the link.
(Another definition for ragamuffins that I've seen is " Urchins".)