Erasmus attended Hoërskool Garsfontein in Pretoria between 2007 and 2011, but never represented the at any high schoolrugby tournaments. After matriculating in 2011, he made the move to Johannesburg to join the academy prior to the 2012 season. He started in twelve of the side's matches during the 2012 Under-19 Provincial Championship, scoring two tries in an 83–3 victory over in their final match of the regular season as the Golden Lions finished in fourth position on the log to qualify for the semi-finals. One of his starts came in the semi-final against, but he could not prevent the side from Cape Town winning the match 24–14. He moved up to Under-21 level in 2013 and played in seven matches for the. He once again finished the regular season by scoring two tries in a match, this time in a 76–7 victory over the s, and once again suffered a semi-final defeat at the hands of Western Province, who beat the Golden Lions U21s 44–41 after extra time. In 2014, Erasmus was included in the squad for the 2014 Vodacom Cup competition. He made his first class debut by coming on as a late replacement in a match against near-neighbours the in a 23–22 victory. After another appearance off the bench against the, Eramus scored his first senior try in a 40–37 victory over the in Johannesburg. He made his first start in their Round Six match against the in Polokwane and scored one of the Golden Lions' sixteen tries in a 110–0 victory. The Golden Lions finished in fourth spot on the Northern Section log to secure a place in the quarter finals, where they met a that topped the Southern Section. Erasmus played off the bench in a 27–20 victory in the match in Durban and also in their 16–15 victory over trans-Jukskei rivals the. He started the final against the in Kimberley in an unfamiliar Eighth man role and could not prevent his side losing the match 6–30 to finish the competition as runners-up. He was named in the squad for the 2014 Under-21 Provincial Championship, but failed to make any appearances in the competition. He returned to action for the Golden Lions in the 2015 Vodacom Cup. He made three appearances as a replacement during the regular season of the competition and started their 29–21 quarter final victory over the. He didn't feature in the semi-final, which saw eventual champions the win the match 43–20. Erasmus was included in the Golden Lions' Currie Cup side for the first time in 2015 Currie Cup Premier Division and was named on the bench for their Round Five match against the in Johannesburg. In the Golden Lions' opening match of the 2016 Currie Cup Premier Division against the, Erasmus scored a try after just 8.5 seconds, the fastest try in the history of the competition.
