With Lance Lynn scheduled to start on Tuesday, it stood to reason the Cardinals would probably need a major contribution out of their relievers if they wanted to push the Dodgers to the brink of elimination. Indeed, the Cardinals did push the Dodgers to the brink, and indeed, the Cardinals did get a lot of help from their relief, with Seth Maness, Carlos Martinez, and Trevor Rosenthal holding the Dodgers scoreless from the sixth. But maybe the Cardinals’ most important reliever wasn’t a relief pitcher at all. Maybe it was another guy who handled the final four innings.

Obviously, the Cardinals had more visible heroes. Lynn himself pitched decently well into the sixth, all things considered. Matt Holliday hit a big dinger. Shane Robinson hit an insurance dinger. Matt Carpenter drove home the first run with a double. There was no one guy who allowed the Cardinals to win — a lot of different parts had to come together just right. Among those parts, though, was Pete Kozma, who helped his team in the playoffs in a much less surprising way than he did a year ago. Last October, for pretty much no reason, Kozma hit. Tuesday, Kozma just played the field.

I think a good way to sum up the Cardinals’ shortstop situation is that Daniel Descalso started in a playoff game because Mike Matheny wanted more offense. Tuesday, Kozma didn’t actually play until the bottom of the sixth, when he went in to play short and Descalso slid over to third. Armed with a lead, this was the Cardinals’ preferred defensive alignment, and though defensive replacements seldom make much of an impact in the later innings, Kozma helped to preserve this game. There’s an argument, not altogether ridiculous, that Kozma turned out to be the Cardinals’ most important player. I don’t know if I believe it, but I might as well advance it.

First of all, by the way, Kozma did bat once. He got hit by a pitch. He didn’t score and it didn’t matter, and it boosted the Cardinals’ win expectancy by about 1%. A little more than that, but it’s hardly worth being more specific. Kozma didn’t do anything good or bad at the plate — he made a difference in the field.

And he made a difference on two plays. The first of them happened almost immediately. It was 3-2 in the sixth, and the Dodgers had one on with one out. In came Maness, up came Juan Uribe, and out went a grounder, to Kozma’s right on a 1-and-1 sinker. Off the bat it looked like the ball could find a hole, but Kozma was able to gobble it up, and then some:

Carpenter, it has to be said, made a hell of a turn with Yasiel Puig flying right at him, and this double play wasn’t turned by one man. But Kozma started it by making a good backhand in the hole. He then made a quick and accurate throw to second while falling away from the bag, a throw in plenty of time to beat the runner, and it was a throw that left Carpenter in good position to get the ball to first quickly. Kozma’s made a habit of this kind of fade-away throw to second and there are few better at it around baseball. This double play ended the Dodgers’ inning.

The Cardinals’ approximate win expectancy jumped from 64% to 73%. And though we can’t know what would’ve happened were it not for Kozma, remember the guy whose place he took:

Descalso is not a good defensive shortstop. He’s not even a particularly good defensive second or third baseman. Kozma is a good defensive shortstop. Descalso might not have been able to turn that same play into anything, were he presented with the opportunity. Let’s quickly review the options.

Had the ball gotten through for a single, putting runners on first and second, the Cardinals’ win expectancy would have dropped to about 56%. Had there been a fielder’s choice at second, their win expectancy would have been about 69%. Had there been an out at first, with the runner advancing to second, their win expectancy would have been about 66%. It’s impossible to isolate Kozma’s contribution, given the lack of a control experiment and given Carpenter’s turn, but this rather easily could’ve been a not-double-play. That would’ve been worse news, for the Cardinals, in a one-run affair.

The next defensive play where Kozma made a difference came an inning later, when the margin had been pushed to 4-2. The Dodgers were dealing with the reality of a game without Hanley Ramirez, but with one out, Nick Punto played the part of a slugger, doubling over Jon Jay’s head. The Cardinals stood about a 79% chance of winning, but the stadium came back alive, having fallen silent after the Uribe double play and Robinson homer. From there it took zero pitches for the Cardinals to make the stadium fall silent once more.

Their win expectancy jumped to 88%. If I heard the postgame show right, this was just the 24th time all season that a runner has been picked off second. It was Martinez who made a perfect throw, and it was Kozma who applied a tag to an over-aggressive Punto. Punto said later it was a lonely feeling, and he was too concentrated on trying to get himself to third with one out. Long-time Punto observers will recall previous instances in which Punto made what appeared to be a boneheaded mistake.

So what was this pickoff play all about?

“That was unbelievable,” Cards manager Mike Matheny said. “That’s instigated by Kozma, so great heads-up play by him.”

More:

The pickoff play was not called. It was all unspoken communication between Kozma and Martinez, which is what made it all the more impressive[…] “I saw him get a few steps off [second base], like he was getting ready to steal,” Kozma said. “And then he stopped. “As soon as he stopped, I got behind him and Carlos saw me. The timing was perfect.”

The earlier double play couldn’t have happened without Carpenter, but it was Kozma who got everything started. The pickoff of Punto couldn’t have happened without Martinez, but it was Kozma, again, who got everything started. The double play highlighted Kozma’s first step, range, and arm. The pickoff highlighted his instincts, creativity, and situational awareness. It required a sudden movement and accurate throw from Martinez, to say nothing of timing and his own awareness, but the attempt was Kozma’s idea. A big hit requires a swing, but also a pitch. This pickoff required an idea and a throw. What wind there was in the Dodgers’ sails abruptly stopped blowing, and it wouldn’t pick back up the rest of the way. They were done in by a double play and a pickoff, two plays in which Pete Kozma was deeply involved.

Because win probability added is so imperfect, and because it’s so difficult to divide up responsibility, we can’t know the true magnitude of Kozma’s contribution. We don’t know what would have happened with a different shortstop, and we’ll never be able to. But Kozma unquestionably played a critical role in the Cardinals’ preserving their late lead. If you want to speak in win-expectancy terms, it’s not too much of a stretch to say Kozma was the game’s most helpful player. Maybe that’s not at all true, I don’t know, but the Cardinals got help from one of their shortstops. At the end of the day, that’s all they can ask for.