The aim of this study is to examine the level of understanding of the principle of fair play by secondary school pupils (n = 827) from the Polish province of Wielkopolska, physical education (PE) students from Poznan University of Physical Education (n = 437), and PE teachers (n = 130). Two structured survey questionnaires were used, namely: The three-level scale known as the Fair Play Moral Dimensions Concept Scale and a Factors of Moral Influence Scale. There were observed differences between male and female students in their comprehension of the principle of fair play regarding the category of sporting activity practiced. The female teachers’ amateur training group more frequently identified the highest level of fair play (32.1% of the examined female teachers) in comparison with their male colleagues. Moreover, differences were noted between boys and girls at the secondary school level. Boys rated the influence of PE teachers and coaches higher, while girls declared that they were more influenced by media and education. For both boys and girls, parents constituted the highest-rated factor of the influence on their moral development. Students also indicated the influence of parents as the highest-rated factor. Among PE teachers, school, as a source of influence on one’s moral development, was awarded higher rates by female than by male teachers. It was observed that parents constituted the highest-rated factor of influence for PE teachers.