Let me see if I can break this down a little more.
Javier Báez (the batter, a Chicago Cub, wearing blue) has just hit the ball. His job is now to run around the bases - 1st, 2nd, 3rd, back to where he started (“home”), at which point he will have scored a point. In practice, he will probably stop partway, wait for the next batter to get a hit, and try to make it home from there.
The Pittsburgh Pirates (in white) are fielding. Their job is to stop the Cubs from scoring by getting them out, by various combinations of catching the ball and tagging people or bases with it.
The scoreboard (top left) shows that one Cub has already made it to second base, so he will resume running now that Javy has a hit. It also shows that two Cubs are out. If a third Cub gets out, their turn to bat will be over, it will be the Pirates’ turn to bat, and the Cubs can’t score anymore (for now, but that’s not relevant).
The Pirate at first base (the first baseman) has the ball. All he needs to do is step on first base while holding it before Javy gets there, and Javy is out. This is probably the number one most common thing a first baseman has to do.
For some reason he starts chasing Javy, presumably trying to tag him with the ball directly. This is a perfectly legitimate way of getting him out, but also completely unnecessary.
This has never happened to Javy before. Unsure what else to do, he just kind of… jogs backwards away from him.
Meanwhile, the Cub who was at second base (Contreras) has made it all the way back to home. Because the Pirates’ first baseman has helpfully walked the ball back home, he can easily toss it to the Pirate at home (the catcher) who will tag Contreras out.
The catcher doesn’t tag him in time.
The umpire signals that Contreras is safe (not out).
Javy also signals that Contreras is safe, just for fun. He’s never been nearby when a teammate makes it home before, and he’s enjoying himself.
Notice that the score has not changed, even though Contreras made it home. That’s because Javy is still technically running to first base. If he gets out before he reaches it, the Cubs’ turn to bat is over, and nothing else that’s happened since he hit the ball matters.
Javy remembers this, and heads back to first base. The catcher throws the ball to another Pirates fielder, who is frantically running to do the first baseman’s job.
Javy is safe at first. Contreras scores (although the scoreboard won’t change for a second).
Javy notices how far away that ball landed, and decides he can make it to second base before anyone picks it up and tags him out.
An offscreen Pirate throws the ball to second base, where another Pirate is ready and waiting to catch it, tag Javy out, and end the Cubs’ turn to bat.
Javy is safe at second. The video doesn’t show it, but he will go on to score as well.
This should have been a very easy out for the Pirates, but through two dropped catches and one truly bizarre decision from the first baseman, they snatched defeat from the jaws of victory and turned it into two points for the Cubs.
The Cubs won this game by two points.
