noun
striking out three consecutive batters
Baseball term for a pitcher retiring three batters in a row via strikeouts in a single inning.
先発投手が初回に三者三振を奪った。
The starting pitcher struck out the side in the first inning.
三者三振でピンチを切り抜けた。
He escaped the jam by striking out three in a row.
三者凡退 means three batters retired in order (not necessarily by strikeouts), while 三者三振 specifically means all three were strikeouts.
Compound of 三者 (three batters) and 三振 (three strikeouts).