Goes back and runs into soldiers and old soldiers (7)

'goes back' is the definition.
(I've seen this in another clue)

'runs into soldiers and old soldiers' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'into' is an insertion indicator.
'soldiers' becomes 're' (Royal Engineers).
'and' means one lot of letters go next to another.
'old soldiers' becomes 'vets' (short for veterans).
're'+'vets'='revets'
'r' put into 'revets' is 'REVERTS'.

'and' acts as a link.