2010-11: Ryan Foss skated for the Mississauga Rebels bantam AAA team in Ontario.
2011-12: Foss played for the Don Mills Flyers minor midget AAA team in the Greater Toronto league. In 62 games he scored 14 goals with 17 assists and 10 penalty minutes.
2012-13: Foss attended the Blyth Academy in Ontario and skated for the school's hockey team. In 68 games he scored 39 goals with 63 assists.
2013-14: Foss was invited to Windsor's training camp as an undrafted free agent and played in 58 regular season games and four playoff contests for the Spitfires in his first OHL season. He scored 13 goals with 19 assists and was +7 with 10 penalty minutes during the regular season. One season after missing the playoffs Windsor finished second in the West Division. The Spitfires faced defending OHL champion London in a first round playoff series and were swept by the Knights. Foss scored 1 goal with 1 assist and was -1 in the four game series. He was ranked 91st amongst North American skaters in Central Scouting's final rankings prior to the 2014 NHL Draft.