Swimmer left equipment in gym (7)
I believe the answer is:
barbell
'equipment in gym' is the definition.
(I've seen this before)
'swimmer left' is the wordplay.
'swimmer' becomes 'barbel' (I've seen this before).
'left' becomes 'l' (common abbreviation).
'barbel'+'l'='BARBELL'
(Other definitions for barbell that I've seen before include "Metal rod used in weighlifting" , "Weight lifter's equipment" , "One gets extremely loaded" , "Weightlifting apparatus" , "equipment in gym" .)