With beagles, a ride turned out nasty (12)
I believe the answer is:
disagreeable
'nasty' is the definition.
('disagreeable' can be similar in meaning to 'nasty')
'with beagles a ride turned out' is the wordplay.
'with' says to put letters next to each other.
'turned out' indicates anagramming the letters.
'beagles'+'a'='beaglesa'
'beaglesa' next to 'ride' is 'beaglesaride'.
'beaglesaride' is an anagram of 'DISAGREEABLE'.
(Other definitions for disagreeable that I've seen before include "Bad-tempered" , "Unpleasant" , "Obnoxious" , "Offensive - peevish" .)