抄録
Purpose : To verify, quantitatively, how difficult the effects of release velocity ［RLV］ and the rotational velocity ［RTV］ of four-seam fastballs are for batters to hit and the effect of the RTV of fastballs on the type of shots in college baseball. Methods : Eight hundred forty fastballs thrown by University A’ s 11 pitchers in the 2017 league games were analyzed. The RLV was measured by a device installed in the stadium. The RTV were estimated by the RLV with the regression model, which was calculated from the data measured by the tracking system during the training session. To assess the difficulty to hit, a logistic regression analysis was used. To examine the type of shots, a chi-square analysis was used. Results : The RLV was significantly associated with swing and miss (odds ratio ［OR］=1.07, 95% confidence interval ［CI］ : 1.01-1.13), after adjusting for the number of strikes, meeting the minimum plate appearance requirement, and batting average. Compared with the moderate RTV fastballs (exceeding 1,928.7 rpm and 2,304.7 rpm or less ; the reference group), the high RTV fastballs (above 2,304.7 rpm) showed a significantly higher OR (1.90, 95%CI : 1.17-3.10) of swing and miss. The OR of shots into the fair zone (0.63, 95%CI : 0.42-0.95) and of making a base hit (0.49, 95%CI : 0.25-0.97) were significantly lower among the high RTV fastballs. A significant interaction was found between the estimated RTV and the type of shot (x2=8.47, df=2, p=.014). Conclusion : The higher the RLV of four-seam fastballs the more likely the result of a swing and miss. The high RTV fastballs result more likely in a swing and miss, less in shots into the fair zone and less in making a base hit, than the moderate RTV fastballs. The low RTV fastballs more likely result in grounders.
