"He probably felt he could continue to pitch," said A's manager Bob Melvin, "but it didn't make any sense to.
"I think it just started bothering him as the game went along. You could tell he was a little bit uncomfortable after the last pitch when he was coming off the mound. His body language wasn't great, so we didn't want to push him."
Catcher Stephen Vogt noticed such body language from the get-go. Kazmir struck out four, but also walked three in the 47-pitch outing, before he was replaced by Dan Otero.
"More grimacy," said Vogt. "His stuff was actually pretty good, but his location was a little erratic, which is unusual for him. You could tell by the look on his face and his body language that he wasn't comfortable."
Kazmir has a history of shoulder issues -- though not recently. Entering Wednesday, he had made 70 starts without a DL interruption since returning to the big leagues with Cleveland in 2013. He went 15-9 with a 3.55 ERA in his first season with the A's last year and exited Wednesday with a 2.93 ERA through 10 outings this season.
The impact of a potentially serious injury could be two-pronged.
The A's, already bit by several ailments this season, can't afford another hit to their rotation. Already, Drew Pomeranz is recovering from a shoulder injury, and Jarrod Parker and A.J. Griffin have suffered setbacks in their Tommy John rehabs.
Moreover, Kazmir's trade value, previously sky-high, could evaporate. The 31-year-old will be a free agent at season's end, like Ben Zobrist and Tyler Clippard, and all three could become prime trade bait should the A's continue skidding down the standings.
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, follow her on Twitter @JaneMLB and listen to her podcast. This story was not subject to the approval of Major League Baseball or its clubs.