Director playing 'Alien' and 'Blade' (7)
I believe the answer is:
bayonet
'blade' is the definition.
(I've seen this before)
'director playing alien' is the wordplay.
'director' becomes 'bay' (I can't justify this - if you can you should give a lot more credence to this answer).
'playing' becomes 'on' (on can mean playing or performing).
'alien' becomes 'et' (extraterrestrial).
'bay'+'on'+'et'='BAYONET'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for bayonet that I've seen before include "Kind of knife attached to a rifle" , "Dagger attached to 26 Across" , "Type of light bulb fitting" , "As soldier" , "Blade fixed to a rifle" .)