His violence will clearly have impact on some boys (5)
I believe the answer is:
rambo
'his violence will clearly' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'impact on some boys' is the wordplay.
'impact on' becomes 'ram' (I can't justify this - if you can you should give a lot more credence to this answer).
'some' says to take the centre.
'boys' becomes 'bat boies' (bat boy is a kind of boy).
The middle of 'batboies' is 'bo'.
'ram'+'bo'='RAMBO'
'have' is the link.
Can you help me to learn more?
(Other definitions for rambo that I've seen before include "Stallone's he-man" , "Tough film hero" , "Stallone film character" , "Film series, starring Sylvester Stallone" , "Character relying on brute force" .)