What determines the success or failure of far-right organisations? This article uses new qualitative data to explain the sudden rise and subsequent decline of the English Defence League, an anti-Islamic, street protest organisation established in the UK in 2009. We explain the rise and fall of the English Defence League through the lens of the theory of collective action to show that the English Defence League initially motivated activism by supplying selective incentives that were enhanced by the participation of others. The pursuit of ‘participatory crowding’ led to indiscriminate recruitment into the organisation that enabled numbers to expand into the thousands, but ultimately caused the English Defence League’s downfall because it resulted in the presence of large numbers of ‘marginal members’ with low levels of commitment whose subsequent exit was decisively destructive. Self-governance mechanisms to ensure greater loyalty from members could have prevented the English Defence League’s decline but would also have limited its initial success.