Dalmatian seen on track (7,3)
I believe the answer is:
spotted dog
'dalmatian' is the definition.
(I've seen this before)
'seen on track' is the wordplay.
'seen' becomes 'spotted'.
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'track' becomes 'dog' (synonyms).
'spotted'+'dog'='SPOTTED DOG'
(Other definitions for spotted dog that I've seen before include "Pudding" , "setter, for example" , "description of a Dalmatian" , "Sweet" .)