Robert Geiser played basketball in Genève for Urania Genève Sport in the 1930s and 1940s where he won several championship titles. He also played for the national team on several occasions, including in 1946, at the European Championships held in Genève. He was selected once again for the national team two years later, one of five members of UGS (alongside Marcos Bossy, Jean Paré, Jean Pollet and Georges Stockly) to compete at the London Olympic Games. There, the Swiss team eventually finished in 21st place, defeating Ireland in a classification match but losing all five round-robin games.
Switzerland