The role of private security staff working in doorwork and crowd control involves the regular assessment of patrons for signs of intoxication, risk, violence and aggression. These assessments are made, often in quick time and with limited opportunity for observation, in queues and in doorways outside licensed venues, when scanning large crowds at major sporting events or concerts, or inside a range of different sites where private security operate. Alongside venue specific dress and behavioural codes, private security use a range of physical and behavioural cues to inform these assessments and categorize the ‘riskiness’ of patrons. This study seeks to identify and examine the physical and behavioural cues that security staff use as predictors of violence propensity to ascertain the effectiveness of such assessments and to help inform better diagnostic practices. The study will conduct both semi-structured interviews with, and a short visual-based assessment of, private security staff working in the doorwork and crowd control sectors to gain an understanding of what patron characteristics they base their judgements on.