Beat soldiers in the open air (7)
I believe the answer is:
outdoor
'in the open air' is the definition.
(I've seen this before)
'beat soldiers' is the wordplay.
'beat' becomes 'outdo' (outdoing is a kind of beating**).
'soldiers' becomes 'or' (Other Rank).
'outdo'+'or'='OUTDOOR'
(Other definitions for outdoor that I've seen before include "Open-air" , "healthy pursuits" , "Located in the open air" , "External" , "Done in the open" .)