Be mistaken during row involving dog (7)
I believe the answer is:
terrier
'dog' is the definition.
(terrier is a kind of dog)
'be mistaken during row' is the wordplay.
'be mistaken' becomes 'err' (I've seen this before).
'during' means one lot of letters goes inside another.
'row' becomes 'tier' (a tier is a row of things).
'err' put inside 'tier' is 'TERRIER'.
'involving' is the link.
(Other definitions for terrier that I've seen before include "Small, short-bodied dog" , "Part-time soldier" , "Short-bodied canine" , "Reserve soldier" , "Bedlington - -" .)