First of petty rules for petitions (6)
I believe the answer is:
pleads
'petitions' is the definition.
(to petition someone is to plead with them)
'first of petty rules' is the wordplay.
'first of petty' becomes 'p' (1st letter of 'petty').
'rules' becomes 'leads'.
'p'+'leads'='PLEADS'
'for' is the link.
(Other definitions for pleads that I've seen before include "Makes appeal or entreaty" , "Appeals or requests earnestly" , "Begs" , "Implores" .)