One following US soccer's development (9)
I believe the answer is:
Here is my best explanation:
'one following' is the definition.
'us soccer's development' is the subsidiary indication.
'development' is an anagram indicator.
'ussoccers' is an anagram of 'successor'.
(Other definitions for successor that I've seen before include "Person taking over from another", "One taking over from another", "Heir", "One follows next in order", "Follower (in post)", "One who follows another", "One following another" and "Person who follows next in order".)