Blackwell, Derbyshire born inside forward Harry Hill played junior football for Birdholme Rovers prior to the First World War and played for New Hucknall Colliery in 1918 before joining First Division Notts County, for whom he had played as a wartime guest in 1918, in May 1919, where he spent the first five seasons of his professional career. He made his Football League debut for them at Manchester City in September 1919, a season in which they would be relegated to the Second Division. In 1922 he was in the Notts County team that lost to eventual winners Huddersfield Town in the FA Cup semi final at Turf Moor and the following season he scored 12 goals as they finished Second Division Champions to return to the top flight.
Sheffield Wednesday bought him in October 1924 after 56 goals in 170 games for The Magpies and he again scored 12 goals as Wednesday won the Second Division Championship in 1926, but back in the First Division he struggled to hold down a place in their first eleven playing only 42 more games in the next three seasons, before transferring to Midland League Scarb0rough in the summer of 1929 after 40 goals in 99 games for The Owls, where he won the Midland League Championship with them in 1930. He returned to League football with Chesterfield in the summer of 1932, playing 11 times and scoring twice, and he then spent the 1933-34 season at Mansfield Town scoring 5 goals in 25 games, from where he joined non league Sutton Town in the 1934 close season, his final club before his eventual retirement.
NB in the image, published in 1925 and stating him as a Sheffield Wednesday player, he clearly is wearing a Notts County shirt, the team he had left a year earlier and it is clearly the same image as used for his 1920 Pinnace card, albeit colourised.