This phrase is confusing me
でもそれを
きめ球にすんのは
ムリだ
The second line, specifically, is giving me trouble. Can anyone shed some light on the phrase, please?

Question

Answer

決め球 means best pitch.
決める is to decide sth, (here it' about the outcome of the game)
球 is obviously a ball, but here it means pitch in baseball.
therefore, 決め球 is a best pitch you can do, that could determines the outcome of the game.

Answer

きめ球  is a baseball term. Also it means "the shot that wins the game". So the literal translation would be: It's impossible to use that to win (the game).