A mistake by the soccer people last month (5)
I believe the answer is:
fault
'a mistake' is the definition.
(synonyms)
'by the soccer people last month' is the wordplay.
'by' is a charade indicator (letters next to each other).
'the soccer people' becomes 'fa' (I can't explain this - if you can you should give a lot more credence to this answer).
'last month' becomes 'ult' (short for 'last month' in correspondence).
'fa' put next to 'ult' is 'FAULT'.
Can you help me to learn more?
(Other definitions for fault that I've seen before include "Blame" , "Defect; culpability" , "Sin, error" , "An incorrect serve in tennis" , "Shortcoming" .)