Trapped in ditch there's a bear (6)
I believe the answer is:
rupert
'bear' is the definition.
(fictional bear Rupert the Bear)
'trapped in ditch there's a' is the wordplay.
'trapped in' means one lot of letters goes inside another.
'ditch there' becomes 'rut' (rut is a kind of ditch. I am not sure about the 'there' bit.).
'a' becomes 'per' (eg 'one a day' means 'one per day').
'rut' enclosing 'per' is 'RUPERT'.
(Other definitions for rupert that I've seen before include "Cartoon strip bear" , "Boy" , "Mary Tourtel's bear" , "It's bought unseen (1,3,2,1,4)" , "Comic strip bear" .)