LEWISBURG, Pa.: An 18-year-old man pleaded no contest Tuesday to participating in a rock throwing episode from an interstate overpass last year that caused grave head and brain injuries to a Stark County middle school teacher.Tyler Porter entered the plea to conspiracy to commit aggravated assault causing serious bodily injury in a deal with prosecutors that calls for a sentence of 22 months to at least 10 years.He’s expected to be sentenced along with two others in the coming months.