A team order established principle (5)
I believe the answer is:
axiom
'established principle' is the definition.
(I've seen this before)
'a team order' is the wordplay.
'team' becomes 'XI' (a football team, from Roman numerals for 11).
'order' becomes 'om' (Order of Merit).
'a'+'xi'+'om'='AXIOM'
(Other definitions for axiom that I've seen before include "truthful statement" , "Maxim, self-evident truth" , "Self-evident statement" , "Generally accepted principle" , "that's self-evident" .)