Standing up for supplied backing on conclusion (9)

'standing up' is the definition.
The definition and answer can be both to do with communicating as well as being present participle verbs.
Perhaps there's a link between them I don't understand?

'supplied backing on conclusion' is the wordplay.
'supplied' becomes 'fed' (feeding is a kind of supplying).
'backing' says the letters should be written backwards.
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'conclusion' becomes 'ending' (synonyms).
'fed' reversed gives 'def'.
'def'+'ending'='DEFENDING'

'for' acts as a link.

Can you help me to learn more?