Athletes penalised for this most deceptive of skills (5,5)
I believe the answer is:
false start
'athletes penalised for this' is the definition.
'most deceptive of skills' is the wordplay.
'most deceptive' becomes 'falsest'.
'of skills' becomes 'art' (I can't justify this - if you can you should give a lot more credence to this answer).
'falsest'+'art'='FALSE START'
(Other definitions for false start that I've seen before include "In which runner is seen to have jumped the gun" , "Unsuccessful beginning" , "may lead to total recall" , "In which someone jumps the gun" .)