Drive away, restricting speed initially, then create a stir (5)
I believe the answer is:
Here is my best explanation:
'create a stir' is the definition.
'drive away restricting speed initially' is the subsidiary indication.
'drive away' becomes 'rout'.
'restricting' is an insertion indicator.
'initially' indicates taking the first letters.
The initial letter of 'speed' is 's'.
'rout' enclosing 's' is 'roust'.
'then' is the link.
(Other definitions for roust that I've seen before include "Rouse, disturb", "Get out of bed maybe", "Wake up", "Stir up (mainly US)", "Treat roughly - disturb", "Root out" and "Create stir".)