Tom, perhaps, cracks up over American film (9)
I believe the answer is:
spartacus
'film' is the definition.
(I've seen this before)
'tom perhaps cracks up over american' is the wordplay.
'tom perhaps' becomes 'cat' (a tom is a male cat).
'cracks' becomes 'raps' (I've seen this before).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'over american' becomes 'us' (abbreviation for United States. I am not sure about the 'over' bit.).
'cat'+'raps'='catraps'
'catraps' back-to-front is 'spartac'.
'spartac'+'us'='SPARTACUS'
Can you help me to learn more?
(Other definitions for spartacus that I've seen before include "Leader of the slave revolt against Rome, 73BC" , "Famous gladiator who led revolt against Rome" , "Roman slave who led an uprising against Roman legions" , "revolutionary leader" , "Roman revolutionary" .)