Surprisingly their purser’s accepting a fund manager’s position (13)
I believe the answer is:
treasurership
'fund manager's position' is the definition.
(the position of a treasurer)
'surprisingly their purser's accepting a' is the wordplay.
'surprisingly' is an anagram indicator.
'accepting' indicates putting letters inside.
'their'+'pursers'='theirpursers'
'theirpursers' anagrammed gives 'tresurership'.
'tresurership' going around 'a' is 'TREASURERSHIP'.
(Other definitions for treasurership that I've seen before include "Financial post" , "banker's office" , "office for financial manager" .)