Ace team needs order in principle (5)
I believe the answer is:
axiom
'principle' is the definition.
(an axiom is a belief or principle)
'ace team needs order' is the wordplay.
'ace' becomes 'a' (abbreviation).
'team' becomes 'XI' (a football team, from Roman numerals for 11).
'needs' is a charade indicator (letters next to each other).
'order' becomes 'om' (Order of Merit).
'a'+'xi'+'om'='AXIOM'
'in' is the link.
(Other definitions for axiom that I've seen before include "Statement regarded as self-evidently true" , "It's taken for granted" , "Generally accepted proposition" , "Universal principle" , "Old saying or precept 95)" .)