Trigger workflow when a sales rep changes the owner

tomsedgwick
Hi there, I want to trigger a workflow if the owner of a contact is changed by a specific user.
 
Context: management wants to know if a sales rep changes the owner of a contact. We don't want the automation to run if the owner is changed by management or by a workflow, only when it is done manually by sales reps.
 
Thanks,
Tom Sedgwick