Former distance measure (6)
I believe the answer is:
league
'former distance measure' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for league that I've seen before include "Group of clubs; distance" , "Old distance measure of about three miles" , "Combination of groups for a purpose, sports clubs perhaps" , "Association of sports teams to organise matches" , "Old measure of distance, about 3 miles" .)