Post from directors welcoming student pair? (7)
I believe the answer is:
'post' is the definition.
(bollard is a kind of post)
'directors welcoming student pair?' is the wordplay.
'directors' becomes 'board' (I've seen this before).
'welcoming' is an insertion indicator (in sense of 'inviting in').
'student' becomes 'l' (as in L-plates for learner drivers).
'pair?' shows that letters should be duplicated (I've seen 'pair' mean this).
'l' doubled is 'll'.
'board' going around 'll' is 'BOLLARD'.
'from' is the link.
(Other definitions for bollard that I've seen before include "Short post barring traffic", "Post on road or quay", "Mooring post - traffic restriction device", "Strong post", "Roadside post".)