投手的臨場表現是影響比賽勝負的關鍵，投手投球內容是破壞擊球員攻擊能力的最大因素，而當壘上有跑壘員時會影響投手的表現。本研究以2009世界青少棒棒球錦標賽為例。探討攻隊佔壘時投手的不同球種之球速、好球率及第一球好球率之差異。研究目的為：探討投手在不同佔壘狀況不同球種之球速、好球率及第一球好球率之差異。結果：（一）不同佔壘狀況球速分析發現，攻隊佔壘時直球平均速度133.12±3.03(km/hr)，無人佔壘時直球平均速度132.94± 4.03(km/hr)(p=.61>.05)；攻隊佔壘時變化球平均速度113.22±4.85(km/hr)，無人佔壘時變化球平均速度112.68± 4.48(km/hr)(p=.65>.05)，無顯著差異。（二）不同佔壘狀況好球率分析，攻隊佔壘時直球平均好球率60.80％，無人佔壘時直球平均好球率66.24％(p=.12>.05)；攻隊佔壘時變化球平均好球率55.15％，無人佔壘時變化球平均好球率60.78％(p=.35>.05)，無顯著差異。（三）不同佔壘狀況第一球好球率分析，攻隊佔壘時直球平均第一球好球率58.10％，無人佔壘時直球平均第一球好球率59.20％(p=.87>.05) ；攻隊佔壘時變化球平均第一球好球率57.90％，無人佔壘時變化球平均第一球好球率61.50％(p=.78>.05)，無顯著差異。結論：由結果顯示，全體在攻隊佔壘與否，對投手表現的差異並無顯著差異。而個人表現上有幾位呈現顯著差異。教練了解比賽可能臨場的狀況，有計畫性安排訓練和模擬比賽，提高選手對比賽中各種變化情境之適應能力。

　　The on-the-spot performance of pitcher is the key of each competition, and hitters’ batting ability be influenced by performance of pitcher. Hence, this study aimed at different speed of ball characteristics, the rate of strike, and the rate of strike of first pitch by researching 2009 16 and under world cup hold by IBAF. The result were followed: 1. by analyzing different on-base situation, when the offensive side on base, the fastball speed of pitcher of defensive side was 133.12± 3.03 (km/hr), while there were not offensive side on base, the fastball speed of pitcher of defensive side was 132.94± 4.03(km/hr) (p= .61> .05). At the same time, when the offensive side on base, the breaking ball speed of pitcher of defensive side was 113.22±4.85(km/hr) , while there were not offensive side on base, the breaking ball speed of pitcher of defensive side was 112.68± 4.48(km/hr) (p= .65> .05), in other side, there is no significant difference.2, by analyzing the rate of strike while different on-base situation, when the offensive side on base, the rate of fastballs’ strike of defensive side was 60.80%, while there were not offensive side on base, the rate of fastballs’ strike was 66.24％(p= .12> .05). At the same, when the offensive side on base, the rate of breaking balls’ strike of pitcher of defensive side was 55.15%, while there were not offensive side on base, the rate of breaking balls’ strike of pitcher of defensive side was 60.78％(p= .35> .05)，in other side, there is no significant difference. 3.by analyzing the rate of strike in the first pitch, when the offensive side on base, the rate of strike in the first pitch was 58.10%, while there were not offensive side on base , the rate of strike of first pitch was 59.20％(p= .87> .05). At the same time, when the offensive side on base, the rate of strike of breaking ball in the first pitch was 57.90%, while there were not offensive side on base, the rate of strike of breaking ball in the first pitch was 61.50％(p= .78> .05), so there was not significant difference. The conclusion was presented: in pitchers’ performance, there was no significant difference no matter the offensive side stay on base or not. However, there was significant difference in personal performance. Therefore, coaches should understand the situation of on-the-spot, and arranging training and practice, so players can improve ability of facing each different situation.