Complex sentence: The Mariners offense, though, was shut out by Blue Jays pitching and Hernández was dealt his twelfth loss of the season, which saw 10 of his losses come because the Mariners were shut out or scored only one run.
Split into simpler sentences: The Mariners offense, however, was shut out by Blue Jays pitching and Hernández was dealt his twelfth loss of the season. Ten of Hernández's twelve losses were in games where the Mariners were shut out or scored only one run.