United’s lead cut by player’s mistake ... (8)
I believe the answer is:
together
'united's' is the definition.
(I've seen this before)
'lead cut by player's mistake' is the wordplay.
'lead' becomes 'tether' (lead can mean a tether or leash).
'cut by' indicates putting letters inside (some letters cut their way into a word).
'player's mistake' becomes 'og' (I can't explain this - if you can you should give a lot more credence to this answer).
'tether' enclosing 'og' is 'TOGETHER'.
Can you help me to learn more?
(Other definitions for together that I've seen before include "Well-balanced" , "United; touching" , "In conjunction, combined" , "Not apart" , "stable" .)