Born in South Africa, Rosenberg moved to Australia as a child and started playing rugby union while a pupil at Sydney Grammar School.

[3] Picked five times for the South Africa national rugby union team between 1955 and 1958, in which he scored two tries,[1] Rosenberg moved to the United Kingdom and changed codes to become a professional rugby league player while studying dentistry at Leeds University.

[3] He rounded off the season playing on the wing in the 25–10 victory over Warrington in the Championship Final at Odsal Stadium, Bradford on Saturday 20 May 1961, in front of a crowd of 52,177.

[5] Known as "the Flying Dentist", Rosenberg left Leeds in 1961 after breaking his jaw and joined Hull FC for whom he played 86 times, scoring 42 tries before retiring from the game in 1963.

After this, Rosenberg turned his hand to other pursuits, including boxing promotion.