Deterioration in sport -- consequently a drop (4,3,4)
I believe the answer is:
wear and tear
'deterioration' is the definition.
(I have seen 'Natural deterioration ' mean 'wear and tear' so perhaps 'deterioration' could also mean 'wear and tear')
'sport consequently a drop' is the wordplay.
'sport' becomes 'wear' (sport can mean to wear or display on one's person).
'consequently' becomes 'and'.
'a drop' becomes 'tear' (teardrop).
'wear'+'and'+'tear'='WEAR AND TEAR'
'in' is the link.
(Other definitions for wear and tear that I've seen before include "Damage from ordinary use" , "Deterioration in normal use" , "Depreciation" , "Two examples of running water" , "General damage from normal use" .)