Saints in poor semifinal surprisingly demonstrating skill (15)
I believe the answer is:
professionalism
'skill' is the definition.
(I've seen this before)
'saints in poor semifinal surprisingly' is the wordplay.
'saints' becomes 'ss' (an abbreviation for saint written twice).
'in' is an insertion indicator.
'surprisingly' indicates an anagram (a surprising ordering of the letters).
'poor'+'semifinal'='poorsemifinal'
'poorsemifinal' with letters rearranged gives 'profeionalism'.
'ss' placed inside 'profeionalism' is 'PROFESSIONALISM'.
'demonstrating' is the link.
(Other definitions for professionalism that I've seen before include "Competence of experts" , "Skill not displayed by amateur" , "Doctor needs to show this skill" .)