Cross out what, right at the bottom? (6)
I believe the answer is:
thwart
'cross' is the definition.
(I've seen this before)
'out what right at the bottom?' is the wordplay.
'out' is an anagram indicator.
'right' becomes 'r' (common abbreviation).
'the bottom?' indicates one should take the final letters (I've seen 'bottoms of' mean this).
The final letter of 'at' is 't'.
'what' with letters rearranged gives 'thwa'.
'thwa'+'r'+'t'='THWART'
(Other definitions for thwart that I've seen before include "Prevent from accomplishing something" , "cross" , "Oppose successfully" , "Defeat" , "seat for oarsman" .)