2009-10: Patrick Sieloff played for the Compuware minor midget team in Michigan. In 37 games he scored 2 goals with 8 assists and had 52 penalty minutes.
2010-11: Sieloff joined the US National Team Development Program in Ann Arbor – appearing in one game for the U18 team and spending the bulk of the year with the U17 squad. Sieloff was scoreless with no penalties in his only game with the U18 team. In 52 U17 games he scored 3 goals with 6 assists and had 76 penalty minutes. He had 1 goal with 2 assists in four games as the USA finished first in the Four Nations Cup in November. In six games at the 2011 World Hockey Challenge he had 1 goal and 1 assist as the USA finished second to Canada Ontario. He skated in all three games as the USA won the 2011 Vlad Dzurilla U18 tournament in Slovakia. Sieloff committed to playing college hockey at Miami in 2012-13.
2011-12: Sieloff played for the NDTP U18 team and won a gold medal with the USA squad at the 2012 U18 World Junior Championship. In 60 games he scored 3 goals with 7 assists and had 113 penalty minutes. Sieloff was plus-three with no points or penalties in six games at the U18 WJC. He was invited to the NHL Draft Combine and was ranked 31st amongst North American skaters in the Central Scouting final rankings and was selected by Calgary in the second round (42nd overall) in the 2012 NHL Draft.
2012-13: Sieloff played 45 games for the Windsor Spitfires in his first OHL season before having to shut things down due to a hip injury in February. The 18-year-old skated for the gold medal-winning USA squad at the 2013 World Junior Championship in Ufa, Russia. He provided a physical presence on the Windsor blue line in his first season, scoring 3 goals with 8 assists and finishing -9 with 85 penalty minutes. The Spitfires finished fifth in the West Division. Sieloff had 1 assist and was an even plus/minus with 2 penalty minutes in six games at the WJC. The USA defeated Sweden, 3-1, in the gold medal game. Sieloff signed a three-year entry-level contract with Calgary in July, 2013.
2013-14: Sieloff had a difficult first pro season — suffering a broken jaw during a fight in a pre-season game with the Flames and the playing just two October games with Calgary AHL affiliate Abbotsford before missing the rest of the season due to a staph infection. Sieloff was +1 wit no points nor penalties in his brief stint with the Heat.
Sieloff is tough, stay-at-home defenseman with a bit of offensive upside to his game. He is solidly built and is a fluid skater who isn't afraid to make use of his size or drop the gloves on occasion. Sieloff is not just a goon as he is already a very good defender in his own zone and has the ability to start plays started from his own end of the ice. He plays with a maturity behind his years and is an effective penalty killer with leadership skills to go along with his grit.
Sieloff attended training camp with Calgary before being assigned to new AHL affiliate Adirondack to start the 2014-15 season. Playing in the AHL as a 20-year-old, he has steadily shed the rust from missing most of the previous season and is supplying both toughness and shutdown positional play for Adirondack. Long-term Sieloff is expected to be an impact player from the backend for Calgary and should be ready to make the leap to the NHL sooner rather than later.