United take a penalty (5)
I believe the answer is:
atone
'united take' is the definition.
Although both the answer and definition are verbs in their base form, I can't understand how they can define each other.
'a penalty' is the wordplay.
'penalty' becomes 'tone' (I am not sure about this - if you are sure you should believe this answer much more).
'a'+'tone'='ATONE'
Can you help me to learn more?
(Other definitions for atone that I've seen before include "Adopt a cause" , "Pay the price" , "Make good" , "Make amends (for something)" , "remedy" .)