Down 2-0 in the best-of-seven NLCS, Game 3 against the Nationals was just about a must-win for the Cardinals (STL-WAS GameTracker). Unfortunately for them, a defensive misplay in the outfield allowed the Nats to expand an early 1-0 lead. 

In the bottom of the third, Adam Eaton put the Nats on the board with a two-out RBI single. Cardinals ace Jack Flaherty, however, got to two strikes on Anthony Rendon and was one pitch away from escaping further damage. Rendon bit on a slider below the zone and lifted it to left field for what seemed like a routine out off the bat. Then this happened: 

Yeah, Marcell Ozuna should've had that, and it certainly looked like he went into his slide a bit early, which put him in an less than optimal position to secure the ball. The official scorer ruled it a double for Rendon, but you can easily argue it should've been an error. After a Juan Soto walk, Howie Kendrick followed with an opposite-field double to make it 4-0. Given the struggles of the St. Louis offense in this series, Kendrick's double may have been the dagger for both game and series. 

The Cardinals for Game 3 started Ozuna in left, Dexter Fowler in center, and Jose Martinez in right. That's a defensive liability at every outfield position. Given the way the playoff baseball is playing deader in the postseason, that's a risk. That didn't necessarily mean anything on this play -- Ozuna, one of the only Cardinals hitting right now, was going to be in the lineup no matter what -- but that weakness on an otherwise strong defensive team got exploited. Let it also be noted that Ozuna made a potentially critical out on the bases following a leadoff double in the second. 

As a partial consequence of all of that, the Nationals find themselves closing in on an all but insurmountable lead in the series. The first pennant in franchise history draws nearer.