Pooh's friend Rabbit's beginning to intervene and provoke (7)
I believe the answer is:
trigger
'provoke' is the definition.
'pooh's friend rabbit's beginning to intervene' is the wordplay.
'pooh's friend' becomes 'tigger' (Winnie the Pooh reference).
'beginning' says to take the initial letters.
'to intervene' means one lot of letters goes inside another (intervene can mean to enter into).
The first letter of 'rabbits' is 'r'.
'tigger' going around 'r' is 'TRIGGER'.
'and' is the link.
(Other definitions for trigger that I've seen before include "One pulled to fire" , "Roy Rogers' horse" , "Part of gun" , "Activating device" , "Cause (device) to operate" .)