Background: Drawing upon Motowidlo et al.'s theory of individual differences in individual performance, the current study aims to contribute to a better understanding of the relationship between conscientiousness and individual soccer performance, by examining whether mental toughness, posited as a characteristic adaptation, acts as a psychological mechanism underlying this link.

Participants and procedure: Relying upon a concurrent validity design, 130 soccer players completed a survey including the measures of conscientiousness and mental toughness. Participants were also instructed to provide a subjective assessment of their individual soccer performance, by self-rating their physical, technical and tactical performance levels. Their objective performance was also measured as the total amount of minutes each player participated in official games, during the first half-season.

Results: The findings showed that conscientiousness and mental toughness represent significant and meaningful predictors of both individual soccer performance measures gathered, i.e. individual soccer subjective and objective performance. As expected, further mediation analyses showed that the influence of conscientiousness on subjective performance is totally indirect, via mental toughness. Still, for the objective performance criterion, only the direct effect of conscientiousness was supported.

Conclusions: These findings support the merits of conscientiousness as a valid predictor of human performance across achievement contexts, namely in sports settings and specifically in the domain of soccer. They also suggest that while this personality factor exerts a direct impact on individual soccer objective performance, it seems to play a more distal influence on subjective performance, by enacting individual mental toughness resources. Major theoretical and applied research implications are discussed.