Speedy expert in a Rolls (5)
I believe the answer is:
racer
'speedy' is the definition.
The answer and definition are not the same part of speech. However, I know that 'speedy' relates to this answer.
'expert in a rolls' is the wordplay.
'expert' becomes 'ace' (ace can informally mean very good).
'in' indicates putting letters inside.
'a rolls' becomes 'rr' (I can't explain this - if you can you should believe this answer much more).
'ace' placed inside 'rr' is 'RACER'.
Can you help me to learn more?
(Other definitions for racer that I've seen before include "one in a hurry" , "American snake" , "Fast mover" , "someone driving very fast?" , "fast-moving vehicle" .)