At Ramsey High School

Yamanashi was a three-sport athlete at Ramsey, where he played soccer, basketball, and baseball. He was named 1st Team All-League, 3rd Team All-County, 1st Team All State Group 2 North Jersey and received All-State recognition. He captained the soccer team, which was the State Sectional Champions, and was the recipient of the Coaches Award. He also played for Parsippany Crew. Yamanashi was a member of the National Honor Society and the Scholastic "R" for four years.