Casilla has some explaining to do after going from first to third on Ryan Flaherty's liner to right field and being doubled off to end the game.
Showalter relayed the explanation from third base coach Bobby Dickerson.
"Bobby, I think, talked to him. Said he thought the ball was a sure double, I believe, but I haven't talked to him yet," Showalter said.
That's exactly what happened. Casilla, pinch-running for J.J. Hardy, didn't lose track of the outs. He thought Flaherty had reached base.
Freddy Garcia (3-4) took the loss after allowing five runs and eight hits in 5 1/3 innings. He may have become distracted after thinking he had struck out Dustin Pedroia leading off the fourth. Plate umpire Jeff Nelson said it was a foul tip, Pedroia singled and Mike Carp belted a two-run homer.
Pedroia told Boston reporters afterward that he hit something, but it was probably the ground.
"Freddy gave us a chance to win," Showalter said. "Had a couple things kind of went against him. We caught some hard-hit balls, too. A double play on a one-hop well-hit ball. He hung in there, gave us a chance.
"There were a lot of things that happened. I think we had a balk that they missed, too. That was pretty blatant, but those things happen. You've got to overcome them. We made some mistakes, too, today."
The foul tip is "a real tough call for an umpire because you can't see," Showalter said. "You can't really definitively see it, so I'm sure you have to talk to them about how they do it mechanically. I'm sure it's by sound or something. The game moves so fast, it's an educated guess, and he made a pitch that he could hit for a base hit on the next one and some things after that. You don't dwell on that too much."
Nelson didn't ask for help on the play.
"He's got a foul tip, and the ball was in the dirt," Showalter said. "The guys at first, second or third aren't going to talk to him about foul tip or not. It's a hard call, whether you call it one way or the other. It's a hard call. The balk's not a very hard call."
The Orioles had two runners thrown out trying to steal, including Nate McLouth with runners on the corners, no outs and Manny Machado at the plate in the fifth. McLouth and Showalter thought Red Sox starter John Lackey committed a balk.
Did the Orioles hurt themselves on the basepaths today?
"No," Showalter replied. "That's just one of those things that's not brought up when they do it (successfully). I trust them. That's one of the reasons why we are where we are competitively, because of guys who have that mentality. I support it, and I'm glad they're doing what they're doing. We're lucky to have some guys who have that mentality. That's what separates them from some people who sometimes question it, because you've got to have that type of mentality to do things in this game."
Garcia still hasn't strung together two consecutive quality starts out of his nine starts.
"I look at it as there are a lot of people who can't string one together, OK?" Showalter said. "That's the way you want to look at it, half-full or half-empty. Freddy gave us a chance to win. Take away a call that went against him with the swing and a miss. Otherwise, he pitched well. As tough as pitching is, sometimes you'll take that. You don't want to drop the standard, but Freddy knows. ... I think he got a little frustrated by the call."
T.J. McFarland relieved Garcia and shut out the Red Sox on one hit over a career-high 3 2/3 innings, with one walk and five strikeouts.
"I thought McFarland was outstanding," Showalter said. "That's about as good as you want to see in execution of pitches. I'm really proud of him today. He gave us a chance to make a run at the end. That was pretty impressive."