Sophus 'Krølben' Nielsen spent most of his career with his local team, Boldklubben Frem.
Nielsen was called up to the first official Danish national team, for the 1908 Olympics. Nielsen scored one goal in Denmark's first ever international , a 9-0 defeat of France B. On October 22, 1908 Denmark played France A and won 17-1. Sophus Nielsen scored a record ten goals; he completed his hat trick in the 6th minute. Denmark went on to win the silver medal, after they were defeated 0-2 by Great Britain in the final.
Back at the Olympics in 1912- Nielsen second from left.
Nielsen has been called Denmark's first professional footballer and in 1910 he and his brother migrated to Germany to play for Holstein Kiel (who finished runners up to Karlsruher in the German National championship that year. I can't find any evidence that Nielsen and the other ten goal man, Gottfried Fuchs, ever faced each other though. Remarkably, at Kiel Nielsen bagged 72 goals in 18 appearances!Neither have I been able to ascertain the meaning of Nielsen's nickname, 'Krølben'.