彼は剛速球投手です。

tbd

He has a good fastball.

なるほど彼は剛速球投手だが、よく荒れる。

tbd

It is true he has a good fast ball, but he is often wild.

なるほど彼は剛速球だが、よくあれる。

tbd

It is true that he has a good fast ball, but he is often wild.