Visitor in clear distress about a late start (6)
I believe the answer is:
caller
'visitor' is the definition.
(caller is a kind of visitor)
'clear distress about a late start' is the wordplay.
'distress' indicates anagramming the letters.
'about' indicates putting letters inside.
'start' suggests taking the first letters.
The initial letter of 'late' is 'l'.
'clear' is an anagram of 'caler'.
'caler' going around 'l' is 'CALLER'.
'in' acts as a link.
(Other definitions for caller that I've seen before include "Visitor" , "One paying a brief visit" , "One visits" , "Someone phoning" , "Person on the line" .)