Injured calf, sore, in the open air (8)
I believe the answer is:
alfresco
'in the open air' is the definition.
(I've seen this before)
'injured calf sore' is the wordplay.
'injured' indicates an anagram.
'calf'+'sore'='calfsore'
'calfsore' is an anagram of 'ALFRESCO'.
(Other definitions for alfresco that I've seen before include "where it's cool" , "Outdoors, meal perhaps" , "exposed to the fresh air" , "Located outdoors" , "Meal eaten in the outdoors" .)