The lengths associations will go to? (7)
I believe the answer is:
leagues
'the lengths associations' is the definition.
'leagues' can be an answer for 'associations' (league is a kind of association). I'm unsure of the 'the lengths' bit.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for leagues that I've seen before include "Old units of length" , "Alliance" , "Groups" , "Unions" , "measures" .)