noun
fastball; heavy fastball; powerful pitch
Baseball term for a pitch thrown with great speed and weight, often implying a fastball that is difficult to hit squarely.
彼は150キロの剛球を投げ込んだ。
He threw a 150 km/h fastball.
剛球に押されてバットが折れた。
The bat broke under the force of the heavy fastball.
速球 is a general term for a fastball, while 剛球 emphasizes power and heaviness, often implying a pitch that overpowers the batter.
Compound of 剛 (strong, firm) and 球 (ball). The spelling 豪球 uses 豪 (powerful, magnificent) with a similar nuance.