Beckett, who was standing in left-center field, went to one knee after he was struck in the left side of the head. Teammates immediately called for the training staff, and he was escorted off the field with his hand on his head.
The Red Sox said the pitcher did not need to be taken to the hospital and was treated at the park. The team initially said Beckett was OK, but he started to experience concussion symptoms and was sent home to rest.
The ball that struck Beckett was hit by Red Sox staffer Ino Guerrero, who was standing in the outfield during batting practice hitting shagged balls with a fungo bat back to a bucket behind second base when one got away from him.
The Red Sox said they will provide another update Tuesday on Beckett, who is scheduled to make his next spring training start Thursday.