A visual search task assesses whether children's understanding of the offside rule is more dependent on domain-specific interests than on gender-specific abilities (Lange-Küttner & Bosco, 2016). Nine- and 12-year-old children (N = 60) were tested with a display of two soccer teams and a target player in an onside, or offside, spatial position. There were 100 trials including four practice trials. One half of the children were tested on the grounds of a football club, while the other half were assessed in a library where they spent their spare time. Both groups were gender balanced. Domain-specific interest was more important than gender differences. The football club members practiced three to four times a week or more and made faster decisions. The 9-year-olds in the football group made reasonable choices, but the 12-year-olds in this group showed significantly better discrimination of onside trials suggesting that they had created a benchmark of what is a correct position that clearly differs from an offside position. This suggests that they were actively engaged in determining a legitimate position and avoiding an offside position that would make a scored goal invalid. The 9-year-olds in the library group could not identify onside position trials as well as offside trials, although this was improved at 12 years. Ballgame practice explained onside/offside task difficulty, but not age differences. It is concluded that the development of a perceptual judgment of a legitimate spatial position in the field is a more systematic approach than giving priority to spatial rule violations.