He soon became a regular in the first-team. In February 1925 Blackburn bought Syd Puddefoot from Falkirk for £4,000. He provided the passes for Ted Harper to score 43 goals in 37 games in the 1925-26 season. This was a new Football League record.
In 1926 Bob Crompton was appointed as manager of Blackburn Rovers. The following year Harper moved to Sheffield Wednesday. Crompton asked Roscamp to replace Harper as centre forward. The move was a great success and that year he scored 11 goals in the league.
According to Mike Jackman (The Essential History of Blackburn Rovers): "the whole-hearted Roscamp was not the most skilful of men but compensated for this with a physical no-nonsense approach."
Blackburn Rovers also did very well in the FA Cup in the 1927-28 season. Blackburn beat Newcastle United (4-1), Exeter City (3-1), Port Vale (2-1), Manchester United (2-0), Arsenal (1-0) to reach the final at Wembley. Roscamp scored four goals including the winner in the semi-final.
Huddersfield Town were hot favourites to win the final. However, in the first minute Roscamp received a pass from Syd Puddefoot. He chipped the ball over the head of Ned Barkas. Billy Mercer, the Huddersfield goalkeeper, attempted to catch the ball. Roscamp collided with Mercer and the ball slipped out of his grasp and trickled into the empty net. Tom McLean added a second after 22 minutes. Alex Jackson got one back for Huddersfield but Roscamp scored his second and Blackburn's third in the 85 minute to give the underdogs a well-deserved victory.
Roscamp also did well the following season finishing top scorer with 17 goals. However, during the 1929-30 season he was switched back to right-half.
In 1931 Roscamp was transferred to Bradford City. After playing 27 games for the club he finished his career at Shrewsbury Town.
Jack Roscamp died in 1939.