  Riots originating during, or in the aftermath of, sports events can incur
significant costs in damages, as well as large-scale panic and injuries. A
mathematical description of sports riots is therefore sought to better
understand their propagation and limit these physical and financial damages. In
this work, we present an agent-based modelling framework that describes the
qualitative features of populations engaging in riotous behaviour. Agents,
pertaining to either a 'rioter' or a 'bystander' sub-population, move on an
underlying lattice and can either be recruited or defect from their respective
subpopulation. In particular, we allow these individual-level recruitment and
defection processes to vary with local population density. This agent-based
modelling framework provides the unifying link between multi-population
stochastic models and density-dependent reaction processes. Furthermore, the
continuum description of this ABM framework is shown to be a system of
nonlinear reaction-diffusion equations and faithfully agrees with the average
ABM behaviour from individual simulations. Finally, we determine the unique
correspondence between the underlying individual-level recruitment and
defection mechanisms with their population-level counterparts, providing a link
between local-scale effects and macroscale rioting phenomena.
