In sports, assessment of skill is important for both evaluation of training and selection of players. The purpose of this study was to examine the utility of a dual-task testing paradigm for assessing the defense skills of softball players. 20 softball players were assessed using 2 testing methods: the dual-task test, and assessment by a coach. In the dual-task test, 20 players were evaluated through 2 different tests. The first was evaluation of catching-throwing and judging situations as separate tasks (single-task test), and the second was evaluation of the 2 tasks at the same time (dual-task test). The catching-throwing and judgement ratings were calculated based on the scores obtained. In assessments by coaches, softball coaches and other sports coaches evaluated the defense skills of the 20 players. The relationship between the dual-task test results and the assessments by softball coaches was analyzed, and this demonstrated a significant correlation between the 2. However, the relationship between the dual-task test results and the assessments by other sports coaches was not significant. These results showed that use of the dual-task test made it possible to assess the defense skills of softball players as effectively as softball coaches. In addition, the relationship between the assessments made by softball coaches and assessments derived from a combination of other sports coaches and the dual-task test showed that defense skills could be assessed by other sports coaches as effectively as by softball coaches, through simultaneous use of the dual-task test. We conclude that the dual-task testing method can help coaches to assess the defense skills of softball players in their teams.