What exactly was going on between Buster Posey and Brandon Belt in the handshake line after the Giants’ 3-1, 13-inning victory Saturday night? Posey and Belt appeared to stare down one another. Then Posey scowled and appeared to snap at Belt. Posey also spent a moment looking upset while conferring with closer Mark Melancon. Giants manager Bruce Bochy confirmed that the disagreement stemmed from something that happened a minute earlier in the 13th, when Posey kept gesturing for Belt to play nearer to the bag in an effort to keep Cardinals baserunner Stephen Piscotty close. Posey appeared exasperated when he couldn’t get Belt’s attention, and glared in the first baseman’s direction after Piscotty stole second base. Approached after Sunday’s loss at Busch Stadium, neither Posey nor Belt would shed any light on their disagreement or even whether they had talked things out. “Whatever happens between us, it’s just going to stay on the field,” Posey said. “I won’t talk about it in the media. That’s something we’ll handle together.” Said Belt: “Yeah, I mean, nothing really happened, so … that’s really all I have to say about it. Stuff happens on the field and we’ll just keep it between us.” This isn’t the first time this season that Posey has been caught on camera apparently upset at Belt. In a game at Dodger Stadium three weeks ago, Posey was spotted in the dugout yelling after Belt didn’t score from second base on a single.