I have every reason to believe it was a badge worn by the RAF boxing team that toured Southern Africa that year.
In what was the worst aircraft accident in South Africa at the time SAAF Airspeed Envoy no. 256 was one of three returning to Pretoria on 6 June 1938 from Rhodesia after a boxing tournament when it entered low cloud near the Limpopo River and had possibly broken up in the air. The two SAAF crew and four RAF boxers were killed.