noun, adverb
after one out
Baseball term. Used to describe the game situation after one out has been recorded in an inning.
一死後、ランナーが二塁に進んだ。
After one out, the runner advanced to second base.
一死後にヒットが出て、チャンスが広がった。
After one out, a hit came and the opportunity expanded.
二死後 means 'after two outs', following the same pattern.
Compound of 一死 (one out) + 後 (after). A straightforward baseball term.