A grid dismantled in planet for festival (5,4)
I believe the answer is:
mardi gras
'festival' is the definition.
(Mardi Gras is an example)
'a grid dismantled in planet' is the wordplay.
'dismantled' is an anagram indicator.
'in' indicates putting letters inside.
'planet' becomes 'mars' (Mars is an example).
'a'+'grid'='agrid'
'agrid' is an anagram of 'digra'.
'digra' going into 'mars' is 'MARDI GRAS'.
'for' is the link.
(Other definitions for mardi gras that I've seen before include "The lead up to fast" , "Shrove Tuesday carnival" , "festive occasion" , "Day for 9 acrosses" , "Shrove Tuesday festival" .)