In 1911 the City senior side asked to play him but were not allowed by the ARU as it was past the 1 July deadline for the transfer of players.

In total he represented Auckland in 8 provincial matches that season, scoring 3 tries, kicking 4 conversions and a penalty for 20 points.

[2] Ifwersen then switched codes to rugby league, joining the North Shore Albions where he debuted for them on 3 May 1913.

Despite serving in the armed forces Ifwersen still managed to turn out for Grafton at stages in every year of the war.

[11] He immediately returned to the rep team, captaining the combined Auckland-North Auckland side against South Africa in his first game back and scoring the only try.

In 1924 his playing in the All Black trial caused considerable controversy with the rugby union seeking to know why he had been allowed to take the field.

After retiring from the playing field Ifwersen began coaching the North Shore first grade side in 1925.

Towards the end of the 1929 season Karl and his brother Neil moved to Piako where they played several matches for the side there against Franklin, Waihi (x2), Hauraki Plains, Matamata, and Waikato.

On 12 October he played in a match for the Thames Valley Power Board against New Zealand Railway and he kicked a penalty, conversion, and drop goal.

In 1933 it was reported that he was coaching the City senior side, who finished the season with a 5 win, 1 draw, 6 loss record.

They went winless in their 6 matches which included 4 in the South Island, which was the first time a team from North Auckland had played there.

Their results were put down to a lack of effort by the players in the Northland region in terms of training and commitment to the sport.

The 1937 season saw Ifwersen secure his first win as North Auckland coach when they defeated Thames Valley 23–9 at Mangaturoto on 23 September.

They lost to Auckland at Dargaville 6-3 and later they had the honour of hosting South Africa for their final tour match of New Zealand.

[17] He was appointed sole selector of North Auckland once again in 1938 and also began coaching the Old Boys clubs senior side.

His first wife was Olga Elizabeth Phillips (1901–1998), before separating and marrying Linda Lewis Flood Brookes (1904-).

He had a daughter with Linda, Marie Jos'e Ifwersen (1928–1990), before separating from her and marrying Katherena Cecilia Imedla Anderson (1894–1954).