Is it permitted or forbidden to play softball on Tisha b'Av?
The Three Weeks by Rabbi Cohen pg 145-146
"One should try not to divert one's mind from mourning on Tishah B'Av. Therefore it is proper to refrain from all pleasurable activities, such as taking a stroll, reading the newspaper, listening to the radio, playing games."
From what Rabbi Jaeger and Rabbi Barclay write in their sefer "Guidelines: over 400 commonly asked questions about the Three Weeks," it appears that there is an outright prohibition on playing softball on Tisha b'Av. As they write, "A person should refrain from all pleasurable activities on Tisha B'Av. For example, one may not go for a stroll, read a newspaper, or listen to the radio."