A delay put back the festival (4)
I believe the answer is:
gala
'festival' is the definition.
(a gala is a festival or party)
'a delay put back' is the wordplay.
'delay' becomes 'lag' (lag is a kind of delay).
'put back' says the letters should be written backwards.
'a'+'lag'='alag'
'alag' written backwards gives 'GALA'.
'the' acts as a link.
(Other definitions for gala that I've seen before include "Public festivity" , "fair" , "Special performance" , "Fête" , "Jamboree" .)