Many chaps are out to be top performers (6)
I believe the answer is:
champs
'top performers' is the definition.
The answer and definition can be both people as well as being plural nouns.
Perhaps you can see an association between them that I can't see?
'many chaps are out' is the wordplay.
'many' becomes 'M' (Roman numeral for a thousand).
'are out' indicates putting letters inside.
'm' inserted inside 'chaps' is 'CHAMPS'.
'to be' acts as a link.
Can you help me to learn more?
(Other definitions for champs that I've seen before include "Munches noisily like abbreviated winners" , "Munches noisily like horse at bit" , "Heaven in Paris?" , "Title holders" , "frets impatiently" .)