、。
If our team's last batter hadn't hit a home run, we would have lost the game.
Literal
Our [attributive-の] team [attributive-の] last [attributive-の] batter [subject-が] home-run [object-を] hit-not-[if-たら], game [to-に] lose-[state-ていた]-[conjecture-だろう]-[reflection-な].
A counterfactual conditional. ~たら in negative form + past conditional consequence (~ていただろう) expresses 'if X hadn't happened, Y would have.' 試合に負ける ('lose the game') — 負ける takes its opponent/match with に. The final だろうな adds a wistful reflection on the near-miss. The ていた form here is past-continuative/perfective used for counterfactual outcome.