Conduct dreadful on court (6)
I believe the answer is:
direct
'conduct' is the definition.
(I know that conduct can be written as direct)
'dreadful on court' is the wordplay.
'dreadful' becomes 'dire' (synonyms).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'court' becomes 'ct' (abbreviation used in road names).
'dire'+'ct'='DIRECT'
(Other definitions for direct that I've seen before include "Creepy-crawly" , "Command to be straight" , "Organise; straight" , "Frank; undeviating" , "Take charge, of company or performance say" .)