A brilliant, feisty and highly skilled small man, Weightman enjoyed an extended career in elite Australian football, despite suffering from diabetes since early adulthood. He overcame doubts about his size and ability to play the game and won many individual awards.
Weightman's early football with Mildura Imperials junior teams included competition best and fairest awards at under 15 and under 17 level, as well as three consecutive premierships. At this time, the north west area of Victoria was zoned exclusively to Richmond. The Tigers relocated Weightman to Melbourne in 1977, when he was 17. He enrolled at Melbourne High School and played for the school team, which won the schoolboy "Herald Shield". These matches were played as curtain raisers to the VFL's Tuesday night series games. Weightman first came under notice in this series. Meanwhile, on Saturdays, he turned out for the Tigers' under 19 side, and played as first rover in the team's victory against Fitzroy in the Grand Final.
Weightman was selected for his senior debut in the opening round of 1978, despite some doubts about his lack of size. He played well in a winning team, but quickly found himself back in the reserves when the team's fortune slumped. This was the pattern for his first two seasons before his career turned around in 1980. After several years in the wilderness, Richmond returned to form due to the improvement of a number of young players such as Weightman. He was now sharing the roving duties with West Australian Robert Wiley. The season culminated in a record win over Collingwood in the 1980 Grand Final, when Weightman had twenty possessions. In the post season, he won Victorian selection for the first time.
The feature of Weightman's game was his constructive handball. He played well in the losing 1982 VFL Grand Final against Carlton.
Weightman represented the Australian state of Victoria, and was state captain in 1987 and 1988 v Western Australia, and against New South Wales in 1990. Overall, he played a total of 20 State of Origin games. It was said he played some of his best football for the State and was one of those rare players - the better the standard the better he would play. His other honours include winning the 1985 Tassie Medal for best player in the State of Origin series and the 1985 Simpson Medal for best player in the Western Australia v Victoria match played in Perth.
Weightman is a diabetic, however this has not stopped him from being active, and in 2005, Weightman continued to have an impact in the EJ Whitten Legends Game at the Telstra Dome with competitors that were mostly around five or six years his junior. He also participated in the 2006 match. Weightman continues to be a regular face at the Richmond Football Club, and has been one of the Richmond runners on match day on and off for the past few years.