Period of green development by company outsiders (7)
I believe the answer is:
regency
'period' is the definition.
(Regency is an example)
'green development by company outsiders' is the wordplay.
'development' indicates anagramming the letters.
'by' means one lot of letters go next to another.
'outsiders' suggests removing the centre (only the letters on the outside of the word remain).
'company' with its centre taken out is 'cy'.
'green' anagrammed gives 'regen'.
'regen'+'cy'='REGENCY'
'of' is the link.
(Other definitions for regency that I've seen before include "Style of British furniture, architecture, etc" , "Periods of the Madness of King George when the Prince of Wales took over" , "Old style" , "historical period" , "Interim ruling period on behalf of another" .)