King showing displeasure when friend interrupts motor sport (10)
I believe the answer is:
rallycross
'motor sport' is the definition.
(form of motor racing)
'king showing displeasure when friend interrupts' is the wordplay.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'showing displeasure when' becomes 'cross' (I can't explain this - if you can you should believe this answer much more).
'friend' becomes 'ally' (an ally is a friend or supporter).
'interrupts' means one lot of letters goes inside another.
'r'+'cross'='rcross'
'rcross' placed around 'ally' is 'RALLYCROSS'.
(Other definitions for rallycross that I've seen before include "off-road racing" , "it's driven in competitively" , "sporting event" , "Motor sport" , "Car event" .)