Convincingly disagree with a redhead on the tube back (5)
I believe the answer is:
rebut
'convincingly disagree' is the definition.
I can't tell whether this definition defines the answer.
'redhead on the tube back' is the wordplay.
'redhead' becomes 'r' (head letter of 'red').
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'back' shows that the letters should be reversed in order.
'tube' back-to-front is 'ebut'.
'r'+'ebut'='REBUT'
'with a' is the link.
Can you help me to learn more?
(Other definitions for rebut that I've seen before include "Overthrow by argument or proof" , "Refure or disprove" , "Drive back" , "Quash" , "Claim or prove to be false" .)