Stephen Strasbrug had a rough outing, and looked off on Friday:

Stephen Strasburg did not look right Friday night. The Giants hit his normally untouchable fastballs all over the park. He fidgeted with his shoulder. He landed funny. After he allowed three runs on five hits in two innings, Strasburg marched down the tunnel to the clubhouse and trainer Paul Lessard followed. Whatever Strasburg told him, the Nationals decided he could not continue. The right-hander’s night ended there. Shawn Kelley relieved him.

…

Strasburg has a long history of injury buildups just like this one. When he fidgets, he feels something. When he gets hit, he is not right. Strasburg had been doing both of those, to a lesser extent than Friday, for weeks.

The Nationals usually make injury announcements after the game. The Giants lead the Nationals 5-2 in the top of the fifth inning.