Long-distance runner to stagger after cutting leg (6)
I believe the answer is:
amazon
'long-distance runner' is the definition.
(long river - rivers run)
'stagger after cutting leg' is the wordplay.
'stagger' becomes 'amaze' (I've seen this in another clue).
'after cutting' means to remove the last letter.
'leg' becomes 'on' (cricket term, fielding positions).
'amaze' with its final letter removed is 'amaz'.
'amaz'+'on'='AMAZON'
'to' acts as a link.
(Other definitions for amazon that I've seen before include "S. America's longest river" , "woman soldier" , "Strong, aggressive woman" , "World's largest river" , "Fighting woman from a great river" .)