A frame of wood at the leisure centre (4)
I believe the answer is:
'a frame' is the definition.
(sash is a kind of frame)
'wood at the leisure centre' is the wordplay.
'wood' becomes 'ash' (I've seen this before**).
'at' is a charade indicator (letters next to each other) (I've seen this in other clues).
'centre' says to take the centre.
The middle of 'leisure' is 's'.
'ash' after 's' is 'SASH'.
'of' acts as a link.
(Other definitions for sash that I've seen before include "Type of sliding window" , "(Uniform) strip; window-frame" , "Item of clothing - frame for glass" , "Ribbon as a symbol of rank" , "Band worn over shoulder or round waist" .)