Starts on some Kafka: a German yarn (5)
I believe the answer is:
skein
'yarn' is the definition.
(skein can mean a length of yarn)
'starts on some kafka a german' is the wordplay.
'starts on' suggests taking the first letters.
'a german' becomes 'ein' ('a' in German).
The first letters of 'some kafka' is 'sk'.
'sk'+'ein'='SKEIN'
(Other definitions for skein that I've seen before include "Coil of wool - flock of geese" , "Coil of yarn - group of flying geese" , "Loose bundle of yarn" , "flock in flight" , "Birds flying" .)