Reptile again let loose around youth centre (6)
I believe the answer is:
iguana
'reptile' is the definition.
(iguana is a kind of reptile)
'again let loose around youth centre' is the wordplay.
'let loose' indicates anagramming the letters.
'around' is an insertion indicator.
'centre' says to take the centre.
The middle letter of 'youth' is 'u'.
'again' is an anagram of 'igana'.
'igana' placed around 'u' is 'IGUANA'.
(Other definitions for iguana that I've seen before include "Lizard Darwin found in the Galapagos" , "cold-blooded customer!" , "Arboreal lizard of S America" , "Arboreal lizard with a spiny crest" , "Something like a monitor" .)