Almost unrestricted speed in run (7)
I believe the answer is:
operate
'run' is the definition.
(I know that run can be written as operate)
'almost unrestricted speed' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'unrestricted' becomes 'open' (similar in meaning).
'speed' becomes 'rate' (the speed at which something happens).
'open' with its last letter taken away is 'ope'.
'ope'+'rate'='OPERATE'
'in' is the link.
(Other definitions for operate that I've seen before include "Conduct business in a theatre" , "Cause to function" , "Work as a surgeon" , "Control, run, a machine say" , "Make function" .)