scriptrunner script to reset single select custom field value on system field assignee change

[Dayanand]

Kindly help us with below script

script to reset single select custom field value on system field assignee value change

Tried behaviour but on edit popup also its resetting single select custom field value which we dont want only on system field assignee value change the custom field value should be reset

def assteam = getFieldByName("Assignee Team")
if (getFieldChanged())

{ assteam.setFormValue([-1]) assteam.setRequired(true) }

[Dayanand]

Any help appreciated?