A leap circling mid-air is ambitious (8)
I believe the answer is:
aspiring
'ambitious' is the definition.
('aspiring' can be similar in meaning to 'ambitious')
'a leap circling mid-air' is the wordplay.
'leap' becomes 'spring' ('spring' can be a synonym of 'leap'**).
'circling' is an insertion indicator (circling can mean going around or containing).
'mid' says to take the centre.
The centre of 'air' is 'i'.
'spring' enclosing 'i' is 'spiring'.
'a'+'spiring'='ASPIRING'
'is' acts as a link.
(Other definitions for aspiring that I've seen before include "Strongly desiring to achieve" , "Hoping" , "Having ambition to achieve greater things" , "Having a strong desire to achieve something" , "Would-be" .)