Cell entrance is blocked by this writer (6)
I believe the answer is:
gamete
'cell' is the definition.
(gamete is a kind of cell)
'entrance is blocked by this writer' is the wordplay.
'entrance' becomes 'gate' (type of entrance).
'is blocked by' indicates putting letters inside (upper walls off glass inside formal).
'this writer' becomes 'me' (the setter of the puzzle is the writer of the clue).
'gate' going around 'me' is 'GAMETE'.
(Other definitions for gamete that I've seen before include "Reproductive cell" , "something seedy?" , "Egg-cell" , "Germ cell in reproduction" , "Male or female germ cell" .)