There is an increasing trend for online sports betting to be identified in gambling treatment services as the principal gambling activity that leads to harmful consequences. The structure of sports betting in online settings has changed extensively in the last 5 years in response to developing information technology, and these changes appear to have increased the inherent risk associated with online sports betting. There is a current need to understand disordered patterns of sports betting in online settings, in order to commence the development of strategies to identify and, where possible, mitigate harm. Therefore, a systematic grounded theory study was conducted, utilising behavioural data and in-depth interviews with a sample of 19 online sports bettors who met the criteria for problem gambling, to produce a substantive outline of the salient sources of harmful participation in modern online sports betting. The core category to emerge was an Online Sports Betting Loop that was facilitated by new structural features of modern online sports betting such as live betting, cash out, micro-event betting and instant depositing. In addition, participants indicated that the immediate accessibility and the ubiquity of online sports betting marketing made it challenging to control sports betting involvement. The emergent findings demonstrate that attention must be directed towards creating mechanisms to reduce patterns of continuous online sports betting by increasing breaks in play in the structure of the activity and enabling customers to restrict usage of features that are associated with disordered play, such as live betting.