Inequitable gender norms can be harmful to girls' and boys' health and sexuality. Programmatic approaches that help renegotiate gendered power relationships are sorely needed. This qualitative study reveals how Parivartan, a sport-based intervention in a Mumbai informal settlement, helped families resist inequitable gender norms that limited girls' mobility in public spaces. Fifteen girl athletes were interviewed in two rounds of face-to-face in-depth interviews. Results identify the strategies girls' mothers used to support their daughters' participation in the programme when they feared their husbands' disapproval. Rather than openly confronting their husbands, mothers worked from within the patriarchal gender order, through its 'cracks', for instance initially hiding their daughters' participation from their husbands. At an appropriate moment, girls' mothers revealed to their husbands about their daughters playing sports, convincing them of the usefulness of the programme. Girls' participation profoundly and positively affected relationships between daughters, mothers and fathers. Over time, parents' trust that girls would not compromise family honour increased, eventually changing the acceptability of girls' playing sport in public in spite of the patriarchal gender order. Concluding remarks offer key implications for effective interventions, highlighting the historical nature of gender transformation processes.