I will run: about to proceed uphill (5)
I believe the answer is:
roger
'i will' is the definition.
('Roger' is used to acknowledge an order)
'run about to proceed uphill' is the wordplay.
'run' becomes 'r' (cricket abbreviation).
'about' becomes 're' (regarding**).
'to proceed' becomes 'go' ('go' can be a synonym of 'proceed').
'uphill' says the letters should be written backwards.
're'+'go'='rego'
'rego' written backwards gives 'oger'.
'r'+'oger'='ROGER'
(Other definitions for roger that I've seen before include "Expression of agreement" , "Boy's name - message understood" , "- - Moore (007)" , "Message received and understood!" , "Message received; name" .)