SAN FRANCISCO — Clayton Kershaw knew right away that something was wrong.
Before the start of the bottom of the fifth inning Thursday afternoon at Oracle Park, Kershaw was throwing warm-up pitches when he said he "felt something kind of lock up" in his lower back.
It was an immediate red flag for a left-hander with a history of back problems, including a month-long absence earlier this season because of SI joint inflammation that caused lower back pain.
