"His lower back's been sore the last week, which we knew," Francona said. "We'd been trying to keep him out of his spikes as much as we can."
Prior to Saturday's contest, the Red Sox played an intrasquad game in the morning, and Francona thinks Beckett slipped on a piece of dirt that was filled in.
"We actually all thought he wanted the rosin bag," said Francona. "And Jason called us out. So rather than pitch a game today, when he could do some further damage, we took him out. He'll be examined thoroughly, as he was today, and, probably more importantly, tomorrow.
"He just wanted to stay out of his spikes [this week]. It happens every year. It happens to probably half our camp. When you're not doing your baseball activities, we actually want them to wear their spikes during our drills, so they don't slip. And once they're done with their drills, we get them out of their spikes, because it's easier on their lower backs."
Beckett was 20-7 -- the Majors' only 20-game winner -- with a 3.27 ERA last season. Watching his ace walk off the mound can cause a manager's heart to leap into his throat.
"Yeah, sure, you kidding me? Probably still is," Francona said. "But there's no reason to ask him to pitch a game down here when we have so much baseball to play. If a kid like Beckett ever threw a pitch and hurt his arm because he's favoring his back, we wouldn't be able to live with ourselves. It's not just Beckett. We wouldn't do that with anybody."
After the game, Beckett, still in the trainer's room, said through Sox media relations director John Blake: "We'll just have to wait and see how it feels tomorrow."
Francona said Beckett had not felt any discomfort while warming up in the bullpen.
"He had a pretty good bullpen [session]," Francona said. "And you got to remember, everybody's back's a little sore. That happens during Spring Training. That's why we have Spring Training. If every time somebody's lower back ached and we didn't play, we'd never have a game. So that's part of it."
Francona said the consistency of the mounds has been an issue.
"We've been fighting -- and this doesn't blame anybody, this field got a lot of play today -- but we've been fighting the consistency in the mounds, in the bullpen and [the main field]," he said. "And, again, that's not to blame anybody. It gets a lot of use. We beat them up. We try to get them to be the same, and today was a hard day to do that, because of our playing a game at 9 this morning."
Beckett left his May 13, 2007, start in Baltimore last season after tearing skin on his right middle finger. He was placed on the disabled list and missed two starts before being activated May 29. Francona said it was too early to determine how this would affect Beckett over the next few days.
"Well, he's not going to pitch in a few days anyways," Francona said. "We'll have a lot better gauge, I'm sure, tomorrow. How sore he shows up, what the medical people say, and again, he'll be examined thoroughly."
Second baseman Dustin Pedroia was at the mound when Beckett left.
"The only thing I saw was his first couple of pitches," Pedroia said. "It kind of looked like something was kind of aggravating him. And he threw a couple more, and that's when he called 'Tek out, Tito and everybody.
"Hopefully, we got a couple weeks left, we can get him back and this isn't an issue, because, obviously, if he's down, that's a huge loss for us. But hopefully, he'll be fine and miss any starts and be doing what he does."
Pedroia said he noticed the Boston ace moving differently on the mound while taking warmup tosses.
"He was just moving around like he was stiff or something," Pedroia said. "That was pretty much what I noticed. ... I don't think anybody wants him to chance that, especially in Spring Training. We don't need him to put up zeros in Spring Training. We need him to do that in the season. To get him out of there and not further [hurt] anything was good."
Pedroia acknowledged it can be disconcerting watching the team's ace walk off the mound.
"You don't want anybody to get hurt in these games, especially when it's our ace," said the second baseman. "So hopefully, it's nothing big and tomorrow he feels a lot better, and hopefully, he'll be fine."