2010-11: Ryan Mantha skated in four games with the Little Caesars midget team as a 14-year-old. He had no points with 2 penalty minutes. In 28 games with the Little Caesars bantam team he scored 4 goals with 10 assists and had 29 penalty minutes.
2011-12: Mantha played forward and defense for the Belle Tire U16 midget minor team in Michigan. In 38 games he scored 8 goals with 14 assists. He had 1 assist with 19 penalty minutes in six playoff games. Mantha was selected by Sault Ste. Marie in the fifth round (97th overall) of the 2012 OHL Priority Draft and signed a tender offer with Sioux City prior to the 2012 USHL Future’s Draft in May. In August 2012 he committed to playing college hockey at North Dakota in 2014-15.
2012-13: Mantha, playing defenseman, skated in 52 games for Sioux City in his first USHL season. He scored 1 goals with 6 assist and was +15 with 48 penalty minutes. The Musketeers finished sixth in the Western Conference; missing the USHL playoffs. Mantha was invited to USA Hockey’s Select 17 Player Development Camp.
2013-14: Mantha began the USHL season with Sioux City before being traded to Indiana in January. He represented the USA in the 2013 Ivan Hlinka Memorial and 2013 World Junior A Challenge tournaments. Mantha had 1 goal with 5 assist and was an even plus/minus with 51 penalty minutes in 29 games with the Musketeers before joining Eastern conference-leading Indiana. Playing with the USA U19 team at the WJAC he was scoreless with 16 penalty minutes in four games. Mantha had 1 assist and was +2 with 27 penalty minutes in five games for the USA U18 team at the Ivan Hlinka Tournament. He skated in the USA Hockey/CCM All-American Prospects Game in September and was ranked 149th amongst North American skaters in the Central Scouting final rankings. The New York Rangers selected Mantha in the fourth round (104th overall) in the 2014 NHL Draft.
2014-15: Mantha, originally headed to the University of North Dakota, played major junior hockey instead, joining to the OHL’s Niagara IceDogs. Slowed by an early season injury, he played 52 regular season games for Niagara. He scored 10 goals with 15 assists and was +21 with 45 penalty minutes. The IceDogs finished third in the Central Division and reached the second round in the playoffs. Mantha scored 1 goal with 5 assists and was +3 with 6 penalty minutes in 11 playoff games.
2015-16: Mantha attended his second training camp with the Rangers before returning to Niagara for his second OHL season with the IceDogs. In 65 regular season games he scored 5 goals with 20 assists and was -1 with 62 penalty minutes. Niagara finished third in the Central Division, defeating Ottawa in a first-round series to reach the second round against Kingston. Mantha scored 2 goals with 2 assists and was +7 with 4 penalty minutes through eight playoff games.
With great size, Mantha is big and can move the puck, which are his greatest virtues. The problem for him has been defensive play, as he is frequently beaten due to lack of foot speed and poor positioning.
Mantha has taken to the open style played by Niagara under coach Marty Williamson during his two OHL seasons with the Ice Dogs, showing an offensive side to go with his physical play in 2015-16. Since he was drafted out of the USHL while committed to playing college hockey, the Rangers have until June 2018 to decide whether to tender Mantha an entry-level contract. He projects as a defense-first defenseman with some puck moving skills.