The Washington Nationals outlasted the Atlanta Braves in 13 innings Monday. The game started late due to rain and didn’t wrap up until well after midnight, which meant that commuters who took Metro to the ballpark couldn’t board a train home.

Many fans who found themselves stranded took to Twitter to vent:

@nationals have to be pretty pissed that @wmata just caused a stadium full of fans to empty out in the 9th inning of a tied game.... #wmata

— Terry C (@itsTERRYble) August 21, 2012

#Nats tied 4-all w/ rival Braves in 9th inn. of crucial game, scoreboard shows last Green #wmata train leaves @ 11:20. Fans stream to exits.

— Chief Welch (@chiefwelcher) August 21, 2012

@placerm All the DCers are mad because #WMATA closes so any metro riders have to choose between end of game and ride home.

— Jennifer Sherman (@jsherman16) August 21, 2012

#Nats/Braves game goes into the early AM. Wonder why #wmata didn’t stay open late like it did after that epic #caps game earlier this year?

— Katherine DuPre (@DCnewskat) August 21, 2012

Pretty absurd that in the capital of the so-called free world there’s no subway system to take ppl home safely this late. #WMATA #Nats

— Sam Jewler (@LuddoftheFuture) August 21, 2012

This isn’t a new issue, and it’s likely to occur again as the season continues. The Nationals have two more weeknight games scheduled this week and eight such games in September and October, to say nothing of games that could run long on weekends (and we’re not even getting into the postseason here).

So here’s a quick rundown of how this happens and why:

It costs Metro $29,500 for each hour it stays open late or each hour it is open early. This isn’t just about keeping the Navy Yard station open, because a fan could be going to any of the 85 other stops within the system. As a result, all stations must remain open and staffed, while all trains have to run in both directions on all five lines, Metro spokesman Dan Stessel said in an e-mail.

The Washington Capitals have an agreement with Metro that has the transit agency stay open late during the playoffs. (Requisite mention of May’s triple-overtime Caps/Rangers game.) The Nationals have no such agreement, though they did make arrangements for a June game against the Phillies, as Dan Steinberg discussed this summer.

A portion of this $29,500 deposit is refunded to the event organizer, though this is based on how many riders enter the system during the extra hour. Metro calculates the number of riders during the extra hour of service and refunds some of that money to the organizers.

The key thing here, according to Stessel, is that event organizers have to make these plans in advance. The agreement has to be signed and a deposit has to be paid before the event, he said.

As Steinberg pointed out in June, any baseball game could theoretically last beyond Metro’s closing time. It’s not like the Nats could have predicted that Monday’s game would start an hour late and last for 13 innings. And they couldn’t have decided at 11:45 p.m. that they would definitely need another hour of Metro service, because the agreement and deposit are needed in advance.

But the Nationals can sign an agreement and put down a deposit for a future game without naming the game in advance, Stessel said. This is similar to the agreement Metro has with the Capitals. The Nationals, like the Capitals, could decide to use that extra hour based on how a particular game is going.

And no, there’s no such agreement in place at this point for any future Nationals games.