After retiring as a player, he was appointed manager of Barcelona by the club president, Joan Gamper, and made his managerial debut on 7 July 1917 in a 3–1 win over CE Europa. He would eventually take charge of the club for 492 games and coached the club during their first "golden age". He survived early calls for his resignation after experimenting with Alcántara as a defender and went on to lead the club to four Campionats de Catalunya and two Copas del Rey. As well as Alcántara, the Barça team under Greenwell also included Sagibarba, Ricardo Zamora, Josep Samitier, Félix Sesúmaga and Ferenc Plattkó. At Barcelona, Greenwell was noted for his innovative approach to tactics, focussing on developing a passing game and building attacks from the back rather than concentrating on dribbling past opponents.
