One attempting to lose runs level (4)
I believe the answer is:
tier
'level' is the definition.
(I know that level can be written as tier)
'one attempting to lose runs' is the wordplay.
'one attempting' becomes 'trier' (someone who tries or attempts to do something).
'to lose' suggests deleting specific letters.
'runs' becomes 'r' (cricket abbreviation).
'trier' with 'r' taken out is 'TIER'.
(Other definitions for tier that I've seen before include "I might draw" , "Storey" , "Bank - row" , "Row - one forming a knot" , "Rite about layer" .)