Milwaukee Brewers second baseman Mike Moustakas tags out Mets catcher...

Milwaukee Brewers second baseman Mike Moustakas tags out Mets catcher Travis d'Arnaud, trying to stretch a single into a double, during the seventh inning of the Brewers' 8-6 victory on Saturday, April 27, 2019, at Citi Field. Credit: Kathleen Malone-Van Dyke

Boos were heard in the fourth inning of the Mets’ 8-6 loss to the Brewers on Saturday night at Citi Field. Travis d’Arnaud had gone down swinging with a runner at second and one out after flying out to strand runners at the corners in the second.

Boos spilled over the Mets’ backup catcher again in the seventh, and he hadn’t even stepped in the batter’s box yet. His average had dropped to .045.

Then came a positive: He lined a single to left. And then a negative: With the Mets trailing by four runs, he was thrown out trying to stretch it into a double. More boos.

Pete Alonso hit a three-run homer later in that inning. “It was an accumulation of everything along with me probably being a little too aggressive down by four runs in that situation,” d’Arnaud said. “Because if he came up with the bases loaded, we tie the game instead of being down by one.”

He also committed a passed ball in the first inning and airmailed a very high throw to second that went into centerfield on a stolen base in the fifth.

After having Tommy John surgery and missing nearly the entire 2018 season, d’Arnaud is hitting .087 — 2-for-23 with two walks and two RBIs. So he understands the fans’ impatience with him, from the offensive end to the defensive end.

“They want me to play better,” d’Arnaud said. “I understand. I’ve got to play better, and I’m just going to keep working.”

Mickey Callaway understands, too. “It’s been a long road,” he said. “A year off is not easy. And then to come back and play at the major-league level sparingly, playing once a week essentially, is a tough task. I’m sure he’s frustrated about it.

“He finally gets a hit up against the wall and then a bad break. [Ben] Gamel throws an unbelievable frozen rope to second. He gets out there. It’s almost like whatever he’s doing is not working. And that’s frustrating for the kid just as much as it is for the fans. It’s tough on everybody.”

General manager Brodie Van Wagenen brought back d’Arnaud on a one-year, $3.515 million deal even though he had been on the disabled list at least once in five of his six seasons.

Entering this season, d’Arnaud hadn’t played since April 8, 2018, as his season ended after only four starts. He underwent surgery to repair the partially torn ulnar collateral ligament in his right elbow on April 17, 2018. After two rehab games with Class A St. Lucie, the Mets activated him three weeks ago.

“Throwing feels fine,” said d’Arnaud, who did throw out Lorenzo Cain trying to steal second in the fourth.

So where’s his game at overall right now? “It’s not where I want it to be,” he said. “But all I can do is just keep working and try to keep a shorter swing and try defensively to just keep working on everything as much as you can, and when it’s your time to go, just be ready to go.”

D’Arnaud’s confidence isn’t shaken. “I feel good,” he said. “Everyone in here keeps me in a good mood all the time. I’ve just got to go out there and just play better. It’s that simple.”

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