Teen messing with gaol gets stretch (8)
I believe the answer is:
elongate
'stretch' is the definition.
(to elongate is to stretch out)
'teen messing with gaol' is the wordplay.
'messing with' indicates anagramming the letters (I've seen 'mess' mean this).
'teen' mixed up with 'gaol' can make 'ELONGATE'.
'gets' acts as a link.
(Other definitions for elongate that I've seen before include "stretcher will do!" , "Make longer" , "Draw out" , "Gone late oddly to extend" , "Widen" .)