Member chosen for XI getting runs (7)
I believe the answer is:
insider
'member' is the definition.
(member of a group)
'chosen for xi getting runs' is the wordplay.
'chosen' becomes 'in' ('you're in!').
'for' means one lot of letters go next to another.
'xi getting runs' becomes 'sider' (I can't explain this - if you can you should believe this answer much more).
'in'+'sider'='INSIDER'
Can you help me to learn more?
(Other definitions for insider that I've seen before include "member of favoured group?" , "in prison?" , "person with the lowdown" , "Member of clique" , "Member of charmed circle" .)