Inna Zaitseva studied players' incentives to exert different levels of effort in different games. The hypothesis of her research suggests that players can express their loyalty to the values of their club by increasing the level of effort in matches, which are considered as principal for the club. One of the explicit criteria for principal matches in football is a derby status of a game. This research demonstrates, that players in Bundesliga in season 2017-2018 exerted a greater level of effort in home derby games, which supports the idea of players’ loyalty to club’s values.