What unusual skill comes across (7)
I believe the answer is:
'across' is the definition.
(athwart can mean across or over)
'what unusual skill' is the wordplay.
'unusual' is an anagram indicator.
'skill' becomes 'art' (both can mean a talent).
'what' with letters rearranged gives 'athw'.
'comes' is the link.
(Other definitions for athwart that I've seen before include "Crosswise" , "What rat is placed across?" , "Transverse; at an oblique angle" , "Crossing" , "wrongly" .)