Uneven treatment of most Irish (3,2,4)
I believe the answer is:
hit or miss
'uneven' is the definition.
(something hit or miss is of uneven quality)
'treatment of most irish' is the wordplay.
'treatment of' is an anagram indicator (letters treated or processed).
'most'+'irish'='mostirish'
'mostirish' with letters rearranged gives 'HIT-OR-MISS'.
(Other definitions for hit or miss that I've seen before include "not having consistent effect" , "Random" , "careless" , "alternatives offered by Juke Box Jury panel?" , "Indiscriminate" .)