Mobile goes off crossing river and mire (7)
I believe the answer is:
embroil
'mire' is the definition.
(thesaurus)
'mobile goes off crossing river' is the wordplay.
'goes off' indicates anagramming the letters.
'crossing' is an insertion indicator.
'river' becomes 'r'.
'mobile' anagrammed gives 'emboil'.
'emboil' placed around 'r' is 'EMBROIL'.
'and' acts as a link.
(Other definitions for embroil that I've seen before include "Involve in argument or quarrel" , "Drag in - bole rim (anag)" , "Involuntarily drag in" , "Involve deeply (in a difficult situation)" , "Tangle" .)