Third base coach Bob Henley waves home Anthony Rendson. (John McDonnell/The Washington Post)

When the Dodgers were in town a few weeks before the end of the regular season, Anthony Rendon hit a double into the left field corner, and Jayson Werth headed for third. Bobby Henley had a flashback.

It was a quick one, not a made-for-TV montage or anything like that. But the memory resurfaced all the same. Last October, when a ball bounced into that left field corner in Game 5 of the National League Division Series and Werth headed his way, Henley waved him home. He was out by yards. The Nationals lost by a run, etching that moment into the Nationals’ still-standing October tombstone as another painful pivot point.

But a year later, in a far less meaningful game, Henley waved Werth home again. This time, he scored, and the moment slid quickly into total obscurity. For Henley, that moment was a reminder of October’s fickle ways, of the tiny moments that can change an entire season this time of year – and the people they change when they do.

“When it works out, it’s great,” Henley said. “When it doesn’t, sometimes it’s sleepless nights. I thought about it all offseason, absolutely.”

Henley watched a replay of the send a few minutes after the play, not so much to torture himself, but for research. None of his decisions, however impulsive a wave of an arm might look, is made entirely in the moment. They are made over months and even years, informed by study and conversations, by split-second calculations computed in a mind trained with hours of information.

A year later, sitting in a dugout in Atlanta with James Taylor humming pleasantly from his iPod, Henley recalled every aspect of that Game 5 situation in detail. By the time of the Werth play, the Nationals had only one hit in scoring position. The other runs came on homers. They weren’t creating runs. They had to push the issue.

He remembered thinking that the Nationals have a lead, plus Max Scherzer on the mound, so any ball that headed to the wall would be a chance to be aggressive. Werth runs fairly well. That was the time to take a chance.

He remembered realizing that the ball was heading back to the infield faster than he thought, hoping Corey Seager would bobble, that something would save him from what he realized too late was a mistake. Nothing did, and he had to answer for it.

“I remember looking at whoever was on deck, starting at him, like right in the eyes right after I got tagged,” Werth said. “That I remember. We both were just like [ugh].”

“But at no point was I like ‘dammit Bobby!’ ” Werth said. “It’s just one of those things. You don’t ever fault people for things like that. It’s just part of the game. It happens.”

But redemption comes swiftly for someone like Werth, even if he has to wait four months before his next at-bat provides the chance. For Henley, who triumphs in obscurity, but errs so publicly, redemption is no guarantee. The work behind it all – his livelihood, the day-to-day grind that prevented him from seeing his daughter play a softball game for years until he snuck away to Alabama on an off-day this year – can be discredited in seconds. One play can cost him his job, though that one didn’t.

For Henley, the work is more extensive than it seems. Asked exactly how he prepares to coach third base each day, Henley began a 20-minute monologue outlining a mental checklist, one longer than any he could fit between the bags of seeds he always keeps in his back pockets.

That mental checklist is broken into sections – information about opposing outfielders, information about opposing team strategy, information about his base runners, information about his team’s strategy, in-game conditions, on-field conditions, and on and on and on.

For example, here is his explanation of the information he accumulates on opposing outfielders:

“You can see every rep on video — like a ball that’s hit down the line that they just lob into second base, how they attack it. Are they aggressively coming at it? Do they square up to it? Are they coming to the side? Are they coming through it as they throw? You can look on balls that they pick up at the wall, do they pick up their target and throw it? Or are they constantly throwing it to where the relay man is moving left or right laterally?”

“One thing I do also is from the point that it touches their glove to the point that they release the ball, I have a thing I do with the computer that there’s a certain amount of clicks I do. It gives you an amount of time-wise, whenever it comes out of their hand – glove-to-hand – how it takes them to release it timewise.”

That is a small sample of the detail into which Henley delves while studying his opponents to increase his chances of sending a runner home successfully. He could, quite frankly, narrate an audiobook on the process – and his Alabama drawl and jovial perspective would make such a book more interesting than it might seem normally.

But his job extends beyond sending runners, to giving signs and hiding signs and serving as an on-field extension of Dusty Baker’s wishes.

“[Third base coach] was the only job I never wanted because you’ve got people in the stands, scouts on TV trying to figure out your signs. You’ve got guys in the dugout on their side, that’s their job to pick up signs if they can,” Baker said. “…That’s a thankless job.”

It’s also a job that requires confidence, the ability to forget and to stick to convictions. Among Henley’s strongest convictions is his commitment to aggressiveness, one so renowned around this franchise that his players made a T-shirt with a poem dedicated to his propensity to send runners home.

General Manager Mike Rizzo and Baker have both described these Nationals as a team built to run with what they hope is the mindset to do it. They want Henley to be aggressive — they want everyone to be aggressive — particularly now, against a Cubs starting rotation that struggles holding runners, at a time when one run can change everything.

“When you have those occurrences every once in a while where it doesn’t work out, you have to be able to continue to keep your chin up, learn from it, and move on,” Henley said. When presented with a similar situation nearly a year later, he pushed the flashback to the back of his mind, ran up the line to get an angle on the play, and told himself “Let’s go.”

“We’re gonna stay aggressive,” Henley remembered thinking. “Werth ended up being safe on that one.”

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