In the past decade mental toughness has been discussed as a significant factor in performance in elite sport. Few studies have explored mental toughness from a behavioral perspective, and no comprehensive lists of mental toughness behaviors have been developed. The aim of the study was to produce a systematic observation checklist of mental toughness behavior in professional soccer. Consistent with existing studies, the results created a systematic observation instrument containing 15 mental toughness behaviors. Practical implications include goal-setting, game analysis and self-modeling interventions where the created checklist could be a practical tool for both coaches and sport psychologists.