Background <p>Smartphone addiction poses a significant threat to adolescent mental health. According to the Compensatory Internet Use Theory and the Stress Buffering Hypothesis, this study investigated whether sports participation moderates the relationship between interpersonal competence and smartphone addiction, and whether this effect differs between football and individual sports.</p> Methods <p>A total of 2,435 primary and secondary school students in China participated in this survey. Data were collected using the Interpersonal Competence Questionnaire, the Athlete Participation Scale, and the Smartphone Addiction Scale. Correlation and moderation analyses were conducted using SPSS 27.0 and PROCESS 4.2 (Model 1 and 3).</p> Results <p>Interpersonal competence was significantly negatively correlated with smartphone addiction (<i>r</i> = -0.192, <i>p</i> &lt; 0.001). While no significant overall moderating effect of sports participation was observed (<i>b</i> = -0.027, <i>p</i> = 0.152), a three-way interaction analysis showed that a significant moderating effect of sports participation level emerged specifically among students participating in football (<i>b</i> = -0.059, <i>p</i> = 0.007). This moderating effect was not significant for participation in individual sports (<i>b</i> = 0.065, <i>p</i> = 0.118).</p> Conclusion <p>Interpersonal competence negatively predicts smartphone addiction, and football participation uniquely moderates this relationship, with the moderating effect strengthening as participation levels increases. These findings suggest that interventions should prioritize socially interactive team sports, such as football, to address adolescents’ social deficits and reduce addiction risks.</p>