Crazed idiot's run out in front of lorry (10)
I believe the answer is:
moonstruck
'crazed' is the definition.
'idiot's run out in front of lorry' is the wordplay.
'idiot's run' becomes 'mons' (I can't justify this - if you can you should give a lot more credence to this answer).
'out' means one lot of letters goes inside another.
'in front' says to take the initial letters (I've seen 'in front of' mean this).
'lorry' becomes 'truck' (I've seen this before).
The initial letter of 'of' is 'o'.
'mons' going around 'o' is 'moons'.
'moons'+'truck'='MOONSTRUCK'
(Other definitions for moonstruck that I've seen before include "Crazy" , "Lunatic" .)