Spurs soar after developing boxing exercise (7)
I believe the answer is:
Here is my best explanation:
'spurs' is the definition.
'soar after developing boxing exercise' is the subsidiary indication.
'after developing' indicates an anagram.
'boxing' indicates putting letters inside ('box' can mean contain, as in to put in a box).
'exercise' becomes 'use' ('use' can be a synonym of 'exercise').
'soar' with letters rearranged gives 'aros'.
'aros' enclosing 'use' is 'arouses'.
(Other definitions for arouses that I've seen before include "Stimulates", "gets excited" and "Inspires".)