Born into a basketball family, Ratcliffe followed his older brother Landon into ice hockey, learning to skate at the age of three and playing in coordinated games two years later.

[4] In his final season with the London Jr. Knights of the Alliance Hockey, Ratcliffe recorded 22 goals and 27 assists for a total of 49 points in 32 games.

[5] He joined the team for the 2015–16 OHL season, scoring his first junior ice hockey goal on October 3, 2015, against goaltender Evan Cormier of the Saginaw Spirit.

[11] In June 2017, the Philadelphia Flyers selected Ratcliffe in the second round, 35th overall, of the 2017 NHL Entry Draft, and he signed an entry-level contract with them in August 2017.

[16] He played two AHL games that season, scoring his first professional ice hockey goal on April 13, 2018, in a 5–2 win over the Bridgeport Sound Tigers.

[18] He finished the regular season with 50 goals and 82 points in 65 games,[19] and he took home the Mickey Renaud Captain's Trophy for leadership in the OHL that spring.

He struggled with the transition from junior to professional level, particularly the greater resistance he faced from opposing skaters, but showed signs of improvement before the COVID-19 pandemic forced the cancellation of the 2019–20 AHL season.