Shifts and stumbles, starting late (6)
I believe the answer is:
alters
'shifts' is the definition.
(I've seen this in another clue)
'stumbles starting late' is the wordplay.
'stumbles' becomes 'falters' ('falter' can be a synonym of 'stumble').
'starting late' means to remove the first letter (the word begins later than normal).
'falters' with its first letter taken away is 'ALTERS'.
'and' acts as a link.
(Other definitions for alters that I've seen before include "Changes, makes different" , "Changes to staler state" , "Changes, modifies" .)