Organisational sponsorship theory (OST) explains how incubators support new ventures by buffering them from competitive pressure and bridging them to external resources, yet it has been developed almost entirely in formal, institutionally designed settings. This study explores how buffering and bridging operate within community markets (CMs) as informal incubators. Drawing on nine hours of field observation across two market days and conversations with 40 consenting stallholders, 23 of whom were interviewed thoroughly, at a UK community market, the study finds that CMs both buffer and bridge stallholders. Buffering happens through organiser-managed protection from direct competition, predictable trading rhythms, socio-emotional capability building, and peer-led resource sharing (a horizontally generated form of buffering absent from formal incubation). Bridging occurs through connections to online channels, multi-venue trading, and external partnerships. Dominant buffering, however, seems prevalent and carries an unintended consequence: communal norms, identity affirmation, and protective structures attenuate incentives for outward growth. This is conceptualised as the small-and-stable condition, the dark side of informal incubation, arising when the buffering-bridging balance is imbalanced in low-formality sponsoring environments. The study extends OST beyond designed incubation and, to our knowledge, offers the first mechanism-level account of CMs as informal incubators.

Highlights
• Organisational sponsorship theory is extended to informal incubation settings.
• Community markets buffer and bridge stallholders as informal incubators.
• Peer-led collective buffering arises horizontally, without organiser design.
• Learning shifts from foundational to relational to embedded across tenure.
• Dominant buffering produces a small-and-stable condition, curbing outward growth.