Fateful date for teams with no capital (4)
I believe the answer is:
ides
'fateful date' is the definition.
(I've seen this in another clue)
'teams with no capital' is the wordplay.
'teams' becomes 'sides' (eg football sides).
'with no capital' means to remove the first letter.
'sides' with its first letter removed is 'IDES'.
'for' acts as a link.
(Other definitions for ides that I've seen before include "March day fatal to Julius Caesar" , "Julius Caesar was told to beware the . . . . of March" , "Fateful day for Caesar" , "May 15, for example" , "Mid-month date in ancient Rome" .)