The use of the Internet has several positive functions, but at the same time it also represents a health risk, especially for adolescents. The increased use of the Internet in recent decades has also been linked to an increase in problematic Internet use, which has now become a global social issue. During the COVID-19 pandemic, Internet use increased even more and influenced adolescents’ habits, leading to an increase in sedentary behaviors. The aim of this study was to understand whether Internet addiction differed between sportive and nonsportive adolescents and between males and females. We analyzed two samples of adolescents, with different behaviors regarding sports practice. Internet addiction was assessed by the administration of a validated questionnaire (UADI) via an online survey. Although all the mean values of both the subgroups fell into the “non-pathological” category, differences between sports groups and sexes were found, with different trends for each one of the five dimensions of Internet use. In conclusion, sportive adolescents generally showed less severe Internet addiction; therefore, encouraging sports practice can help to fight wrong habits related to a sedentary lifestyle. The promotion of sports practice in these ages is therefore a priority aspect, especially in females, who showed a general predisposition to escape from reality in comparison to males.