Scheduled League clash? (4)
I believe the answer is:
duel
'clash?' is the definition.
(thesaurus)
'scheduled league' is the wordplay.
'scheduled' becomes 'due' (I've seen this in other clues).
'league' becomes 'l' (abbreviation).
'due'+'l'='DUEL'
(Other definitions for duel that I've seen before include "Contest between two people, perhaps with weapons" , "Contest between two with deadly weapons" , "Gentlemen's disagreement" , "Combat to settle a row" , "Combat between two people in matter of honour" .)