How overcrowding very annoyingly starts in cells (3)
I believe the answer is:
ova
'cells' is the definition.
(ovum is a kind of cell)
I cannot understand how the remainder of the clue works.
(Other definitions for ova that I've seen before include "Release of women" , "Female egg-cells" , "Female gametes" , "Female egg cells" , "Likely end for Russian Fed cup players" .)