Second in command extremely upset and cross about being in the open air (7)
I believe the answer is:
outdoor
'being in the open air' is the definition.
(I've seen this before)
'second in command extremely upset and cross' is the wordplay.
'second in command' becomes 'o' (o is the second letter in command).
'extremely' suggests removing the centre.
'and' says to put letters next to each other.
'cross' becomes 'door' (a door is a kind of cross**).
'upset' with its centre removed is 'ut'.
'o'+'ut'+'door'='OUTDOOR'
'about' is the link.
(Other definitions for outdoor that I've seen before include "Done in the open" , "This sport is not under a roof" , "Not done in the house" , "Al fresco" , "Not inside" .)