Sluggish swim, rubbish doing the backstroke? (6)
I believe the answer is:
torpid
'sluggish' is the definition.
(I've seen this before)
'swim rubbish doing the backstroke?' is the wordplay.
'swim' becomes 'dip' (dip is a kind of swim).
'rubbish' becomes 'rot' (I've seen this before).
'doing the backstroke?' says the letters should be written backwards.
'dip'+'rot'='diprot'
'diprot' reversed gives 'TORPID'.
(Other definitions for torpid that I've seen before include "hibernating?" , "Sluggish, dormant" , "Lethargic - drop it (anag)" , "Slow, dull" , "Physically inactive" .)