Grobbelaar was born and grew up in Paarl. He attended and played rugby for Paarl Gymnasium and was selected for the Western Province squad for the 2015 Under-18 Craven Week tournament. His team won the main match at the tournament held in Stellenbosch, beating Eastern Province 95–0 in the final. After the Craven Week tournament, Grobbelaar was selected for the South Africa Schools squad that participated in the 2015 Under-18 International Series. He started all three of their matches; he scored a try in their 42–11 win over Wales in their first match[2] and helped his team to wins over France[3] and England[4] in the other two.
After school, he moved to Pretoria to join the Blue Bulls academy. He played for them at Under-19 level in 2016, and the following year he was selected in the South Africa Under-20 squad for the 2017 World Rugby Under 20 Championship. He started all five matches at the tournament, helping his side to a 23–23 draw against France,[5] a 38–14 victory over Georgia[6] and a 72–14 win over Argentina (a match in which Grobbelaar scored two of South Africa's eleven tries)[7] as South Africa topped Pool C to qualify for the semi-finals. A 22–24 defeat to England in the semi-finals ended their hopes of winning the competition,[8] but they bounced back in the third-place play-off to beat France 37–15, with Grobbelaar scoring a further two tries.[9]
He made his domestic first class debut shortly after his return to South Africa, coming on as a replacement in the Blue Bulls' 54–22 victory over the Golden Lions in their 2017 Currie Cup Premier Division Round Three match.[10] He became a regular on the Blue Bulls' replacement bench during the season, making a total of ten appearances. He also scored three tries during the season, in matches against Western Province,[11] the Golden Lions[12] and the Free State Cheetahs.[13]