KANSAS CITY -- The Yankees remained miffed at a disputed home run call in Wednesday's 5-4 loss to the Royals at Kauffman Stadium, saying that they are not sure the umpires properly understood the ground rules involved.

Yankees manager Joe Girardi said that he was second-guessing himself for accepting the word of crew chief Dana DeMuth, who credited Royals designated hitter Billy Butler with a solo home run after reviewing a play in which the ball struck the left-field wall and bounced back into play.

The replay showed that Butler's drive struck the top of the padded fence in left-center field and struck a small fence behind the wall before popping in the air.

"He said it's clearly a home run," Girardi said of DeMuth. "Maybe I erred. I believed the umpire."

DeMuth declined comment on behalf of the umpires to a pool reporter, but after the game, all four members of the crew were led to the warning track by umpiring supervisor Steve Palermo to inspect the layout of the fences.

The discussion is likely to be procedural. Girardi said he believes he had to file a protest immediately, and since he did not, the Yankees' loss would appear to be final.

"The reason I didn't is because I believed the umpire that he knew the ground rules," Girardi said. "I probably should have [protested]."

Yankees third-base coach Mick Kelleher said that he had discussed the wall situation with DeMuth before Monday's series opener, and the interpretation seemed different than the one applied on Wednesday.

Kelleher said that his understanding was that the ball needed to also clear a chain-link fence and padded railing to be a home run, a topic he said they discussed when exchanging lineups on Monday.

"We went over the ground rules and they were pretty explicit and clear, but there was one question that I had: it was about the top rail in left-center field," Kelleher said.

"It was padded; the ball had to leave the ballpark. We talked about that twice. ... It doesn't make sense to me. The ball never left the ballpark, so how could it be a home run?"

Yankees closer Mariano Rivera was uncharacteristically irate with the ruling, charging from the clubhouse after seeing it on television and barking at the umpiring crew after Butler's homer was upheld.

"I mean, that cost us the game," Rivera said. "Tied game, you know? I understand we're human, but come on. You have replays and get the call wrong? That's unacceptable."

Rivera also pointed out that Butler grabbed his helmet in the Kansas City dugout during the review, as though he expected to be sent to second base.

"The guy was ready to go to second base," Rivera said. "The guy has a helmet in his hands, ready to go back to second base, and all of a sudden, you call a home run? Come on."

Butler said he wasn't sure what to expect while the play was being reviewed.

"I got told some things," Butler said. "We didn't really have a good angle on that, so [the umpires] have a better view than we do and they have to call New York and get a ruling and look at it. So if they tell me it's a home run, it's a home run."

Immediately after the play, Yankees outfielders Brett Gardner and Curtis Granderson signaled the umpires, trying to tell them that the ball hadn't cleared the fence.

Both Gardner and Granderson said that the Yankees had other opportunities to win the game and wouldn't hang the loss completely on that one play, but they remained slightly miffed at the odd setup.

"I looked at the replay, and sure enough, it did hit that chain-link fence," Gardner said. "If that's not part of the fence, then it's a home run.

"I just don't understand why that little piece of fence is there. It probably could lead to a lot of controversy over the years."

Girardi said that he would call the Major League Baseball offices on Thursday for clarification on DeMuth's ruling.

"If he's right, he's right and we lost the game," Girardi said. "If he's wrong, it's real unfortunate."