Something Blue gets an occasional Epsom run (4)
I believe the answer is:
porn
'something blue' is the definition.
(blue can mean pornographic)
'an occasional epsom run' is the wordplay.
'an occasional' means one should take alternating letters (letters taken at regular intervals).
'epsom'+'run'='epsomrun'
The alternating letters of 'epsomrun' are 'PORN'.
'gets' acts as a link.
(Other definitions for porn that I've seen before include "Obscene material" , "blue material" , "Lewd material (abbr)" .)