Arrive guarding soldiers with rubbish report (10)

'report' is the definition.

'arrive guarding soldiers with rubbish' is the wordplay.
'arrive' becomes 'come' (synonyms).
'guarding' indicates putting letters inside.
'soldiers' becomes 'men' (men can mean a group of soldiers).
'with' means one lot of letters go next to another.
'rubbish' becomes 'tat' (low-quality items or material).
'men'+'tat'='mentat'
'come' enclosing 'mentat' is 'COMMENTATE'.