Blackadder was named in the squad for the 2018 Super Rugby season. He made his debut against the in Round 10 and was later named Crusaders rookie of the year. Blackadder played every minute of the 24–13 win over the in the 2021 Super Rugby Aotearoa final as the side won their fifth title in a row. After an outstanding season Blackadder was voted Champion Crusader of the Year by his teammates at the 2021 Crusaders awards. Blackadder suffered a season ending injury late in the 2022 Super Rugby Pacific season as the Crusaders went on to a 7–21 win over the in the final.