Background: The transition to adulthood may involve experiences of risk and harm -- including, for some young people, abuse, violence or exploitation in peer and community contexts. In the UK, such extra-familial risks and harms have prompted safeguarding responses in policy and practice. However, safeguarding conceptualisations are significantly different for young people under 18 than for those over 18, leading to service and system gaps in transition. The concept of Transitional Safeguarding seeks to address this, advocating for more integrated approaches that centre the needs, voices and lived experiences of young people. Objectives: Based on findings from a study on early-stage innovation developments aligned with Transitional Safeguarding, this paper considers issues and dilemmas linked to reconceptualising 'safeguarding' so as to better protect young people experiencing extra-familial risks and harms during transition to adulthood. Methods: A 4-year study followed safeguarding innovation developments in selected local areas in England, based on a qualitative case study approach that involved ethnography, interviews and documentary analysis. Findings: The paper highlights gaps in safeguarding services and systems for young people around age 18, when support may either significantly decrease or stop altogether. The intersecting dynamics of risks, harms and unmet needs point to the importance of multi-agency collaboration, beyond service-centric threshold definitions. The need to systemically and systematically involve young people in support and innovation development is also emphasised. Conclusions: The boundary-spanning change which the Transitional Safeguarding approach advocates requires significant shifts to create conditions capable of addressing risks and harms during transition to adulthood, as well as their structural drivers. Navigating these shifts remains a key challenge for local services and systems engaged in Transitional Safeguarding innovation, and their efforts need to be supported by policy frameworks and adequate funding.