Lack of practice, with son no longer in the groove (3)
I believe the answer is:
rut
'the groove' is the definition.
(rut is a kind of groove)
I don't understand the remainder of the clue.
(Other definitions for rut that I've seen before include "spell of arousal" , "humdrum activity" , "deer find it exciting" , "Deep track or tedious routine" , "Undeviating routine" .)