I'll call it "breaking cover” (7)
I believe the answer is:
visitor
'i'll call' is the definition.
I can't tell whether this defines the answer.
'it breaking cover' is the wordplay.
'breaking' becomes 'visor' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'cover' is an insertion indicator.
'it' put into 'visor' is 'VISITOR'.
Can you help me to learn more?
(Other definitions for visitor that I've seen before include "One coming to call" , "Person turning up" , "Someone calling (again at 23?)" , "Caller, guest" , "One coming calling" .)