(Portland, OR)  --  A petition is circling to reinstate a popular Portland teacher who was placed on leave over an unauthorized walkout.  A district spokesman says Chris Riser was put on leave Friday from Ockley Green Middle School after the student walkout last month.  The protest reportedly centered on the police shooting of a 17-year-old a year earlier.  "The Oregonian" reports that more than 13-hundred signatures have been gathered on a petition in an effort to have Riser reinstated.  The walkout was called an "unauthorized" action not in keeping with district policies.