Most boring cricket match involving Durham's tail-enders (6)
I believe the answer is:
tamest
'most boring' is the definition.
Both the answer and definition are superlative adjectives. Perhaps you can see a link between them that I can't see?
'cricket match involving durham's tail-enders' is the wordplay.
'cricket match' becomes 'test' (a test is a kind of cricket match).
'involving' means one lot of letters goes inside another.
'durham's tail-enders' becomes 'am' (I can't explain this - if you can you should give a lot more credence to this answer).
'test' enclosing 'am' is 'TAMEST'.
Can you help me to learn more?
(Other definitions for tamest that I've seen before include "Meekest or least wild" , "Least wild, most domesticated" , "Least exciting" , "Most docile" , "Most restrained or quiet" .)