Kind found not offside in the box (11)
I believe the answer is:
considerate
'kind' is the definition.
(similar in meaning)
'not offside in the box' is the wordplay.
'not offside' becomes 'onside' ('onside' is the opposite to 'offside').
'in' means one lot of letters goes inside another.
'the box' becomes 'crate' (crate is a kind of box).
'onside' placed within 'crate' is 'CONSIDERATE'.
'found' is the link.
(Other definitions for considerate that I've seen before include "Showing concern for the feelings of others" , "Kind" , "Thinking of others" , "Showing care" , "Unselfish" .)