Out of practice but reliable without leader (5)
I believe the answer is:
rusty
'out of practice' is the definition.
(I've seen this before)
'reliable without leader' is the wordplay.
'reliable' becomes 'trusty' ('trusty' is associated in meaning with 'reliable').
'without leader' means to remove the first letter.
'trusty' with its initial letter taken off is 'RUSTY'.
'but' acts as a link.
(Other definitions for rusty that I've seen before include "(Of iron) affected by damp" , "Affected by corrosion - out of practice" , "Reddish," , "Oxidised, corroded" , "affected by inactivity" .)