Teams start to struggle before day in Rome (5)
I believe the answer is:
sides
'teams' is the definition.
(eg football sides)
'start to struggle before day in rome' is the wordplay.
'start to' indicates taking the first letters.
'before' means one lot of letters go next to another.
'day in rome' becomes 'ides' (Roman calendar term, as in the Ides of March).
The initial letter of 'struggle' is 's'.
's'+'ides'='SIDES'
(Other definitions for sides that I've seen before include "Outer edges, left and right" , "More than one team" , "Teams or flat surfaces" , "Opposing factions or facets" , "Aspects" .)