Sucker with no science subjects upset (5)
I believe the answer is:
straw
'sucker' is the definition.
(I've seen this before)
'with no science subjects upset' is the wordplay.
'with' becomes 'w' (abbreviation).
'no science subjects' becomes 'arts' (the arts are not science subjects).
'upset' says the letters should be written in reverse.
'w'+'arts'='warts'
'warts' backwards is 'STRAW'.
(Other definitions for straw that I've seen before include "Bedding material for horses etc" , "Stems left after grain has been removed" , "Animal bedding" , "Dried grain stalk" , "Residue of cereal crop" .)