Blowing hard, losing weight in a type of racing (4)
I believe the answer is:
indy
'blowing hard losing weight' is the definition.
The definition suggests a singular noun which matches the answer.
'in a type of racing' is the wordplay.
'a type of racing' becomes 'dy' (I can't explain this - if you can you should believe this answer much more).
'in'+'dy'='INDY'
Can you help me to learn more?
(Other definitions for indy that I've seen before include "Abandon, discard" , "500-mile US motorcar race" , "US form of motor racing" , "A US motor sport" , "- - Car racing (in US)" .)