First of all playing average round — this the score? (3)
I believe the answer is:
par
'this the score?' is the definition.
(par is a kind of score)
'first of all playing average round' is the wordplay.
'first of all' says to take the initial letters.
The first letters of 'playing average round' is 'PAR'.
(Other definitions for par that I've seen before include "Usual score at golf" , "Accepted level" , "level footing" , "Average or normal score" , "Average standard" .)