Reserve German is stopping ball (8)
I believe the answer is:
distance
'reserve' is the definition.
(I've seen this before)
'german is stopping ball' is the wordplay.
'german' becomes 'ist' (I can't justify this - if you can you should believe this answer much more).
'is stopping' is an insertion indicator (stopping can mean blocking a gap).
'ball' becomes 'dance' (ball can mean an event for dancing).
'ist' going inside 'dance' is 'DISTANCE'.
Can you help me to learn more?
(Other definitions for distance that I've seen before include "What's kept in reserve" , "standoffishness" , "See 3" , "Range" , "Ascend it from one point to another" .)