Thousands in disgrace abroad took part in untidy melee (10)

'took part in untidy melee' is the definition.
Although both the answer and definition are past participle verbs, I cannot see how they can define each other.

'thousands in disgrace abroad' is the wordplay.
'thousands' becomes 'mm' (the Roman numeral for a thousand written twice).
'in' indicates putting letters inside.
'abroad' indicates an anagram (abroad can mean moving around).
'disgrace' with letters rearranged gives 'scriaged'.
'mm' placed inside 'scriaged' is 'SCRIMMAGED'.

Can you help me to learn more?