Richard helped Millwall towards becoming 2000–01 Second Division Champions but was forced to watch from the stand as Millwall reached the 2004 FA Cup Final in his final season. A striker, Sadlier scored 34 goals in 103 starts for Millwall. In an interview with the BBC, Mark McGhee named Sadlier as potentially the best young centre forward he had ever worked with in his managerial career. In 2003, Sadlier retired from the professional game due to a hip injury at the age of 24.