What starts scratching this spot on priest's ball? (6)
I believe the answer is:
sphere
'ball?' is the definition.
(ball is a kind of sphere)
'what starts scratching this spot on priest's' is the wordplay.
'what starts' suggests taking the first letters (the letter that starts the word).
'this spot' becomes 'here' (I've seen this in another clue).
'on' is a charade indicator (letters next to each other).
'priest' becomes 'p' (ecclesiastical abbreviation).
The initial letter of 'scratching' is 's'.
'here' after 'p' is 'phere'.
's'+'phere'='SPHERE'
(Other definitions for sphere that I've seen before include "Perfectly round solid geometric figure" , "Shape of the Earth" , "All-rounder" , "Social circle" , "Perfect round" .)