[1] Blackman began his career at Afewee Academy[2] in Brixton before joining as a trainee with Arsenal, moving to Tottenham Hotspur and then signing for Portsmouth at the age of 16.
[5] Blackman started his professional career by signing a two-year contract with Bristol City after his release by Portsmouth.
[9] After declaring he wanted to "sort his life out",[4] Blackman signed for Conference National club AFC Wimbledon on 1 June 2010,[9] and made his debut in their 1–0 away win against Southport on 14 August;[10] however, after a handful of appearances, Blackman was declared surplus to requirements and was replaced by Chris Bush,[11] and subsequently Gareth Gwillim.
Blackman thanked Neil Lennon for saving his football career after a troubled year and admitted he had to show humility and mental strength to make a breakthrough.
[24] Manager Terry Butcher revealed he terminated Blackman loan spell because of his poor attitude and discipline.
[26] He made his debut in the club's first game of the new season at Southend United,[27] and also started in the next two matches before losing his place in the team.
[28] Blackman scored the first goal of his career in a Football League Trophy tie against Swindon Town,[29] but he remained on the fringes of the team and made his ninth and final appearance for the club in October.
[31] In March 2014, Blackman joined Conference South club Dover Athletic on non-contract terms and scored on his debut against Dartford in the Kent Senior Cup.