Cubs' difference-maker? Might be David Ross (and his .176 average)

— -- For five months, the backup catcher struggling to hit .190 watched the All-Star first baseman play. He celebrated the towering home runs, marveled at the Gold Glove defense and the way Anthony Rizzo's individual successes lifted the rest of the Chicago Cubs. But over the course of the season, David Ross also came to know the rare moments when he didn't think Rizzo was giving his all. And for some reason, the finale of a critical, mid-September series in PNC Park against the Pittsburgh Pirates, the team the Cubs were chasing for the right to host the National League wild-card game, was one of those moments.

Ross wasn't going to let it slide.

A 14-year major league veteran, Ross understands as well as anyone the challenges of getting up for every game - especially a Thursday matinee at the end of an eight-game road trip. But he also realized Rizzo's importance to the psyche of the clubhouse. If Rizzo felt he could take a day off and coast, others in the clubhouse might feel the same. Ross couldn't let it happen.

With the bases loaded and nobody out in the first inning, Rizzo rolled over a 1-1 pitch from Charlie Morton, a pitcher with a career 4.54 ERA, grounding into a double play. Morton is "a pitcher I would expect [Rizzo] to have a good day against," Ross said. Two innings later, Rizzo walked with one out and advanced to third on a double by Kris Bryant. But Ross thought he could have scored. The inning ended with Rizzo stranded on third. In the dugout later, Rizzo asked if Ross thought he could have scored. That's when the 38-year-old sounded off.

"You want my honest opinion?" Ross said. "I don't think you came ready to play today. I don't see the intensity in your game. I don't see the intensity in your at-bats. I don't think you're bringing it."

Rizzo didn't like what he was hearing. Ross had played in less than half the Cubs' games. He'd struck out twice as many times as he'd gotten a hit. Like most team sports, a baseball player's clubhouse clout is generally tied to his on-field performance. But Rizzo respectfully listened to Ross. He took it all in. And two innings later, facing Morton for a third time, Rizzo crushed a 1-0 pitch into the right field bleachers to give the Cubs a 5-4 lead in a game they eventually won 9-6. After his home run trot, Rizzo made a beeline to Ross, planted his head into the catcher's chest and started punching him in the gut.

"I started screaming at him," Rizzo said. "It's one of those things ... [Ross] doesn't demand respect -- he earns it. He lets you know in a nice way, and he'll get on you in a rough way if he needs to. I tell him all the time I just want to go out and prove to him I can bring it everyday."

What is it about Ross that made Rizzo listen? How exactly did a 38-year-old backup catcher who has hit .190 the past three seasons become the Cubs' clubhouse leader? Why is Ross the player manager Joe Maddon refers to as a "force multiplier," someone who "brings out courage and strength in other people" and is an irreplaceable piece of the 2015 Cubs?

"It's hard to put into words," Rizzo said. "It's something that the guys that sit behind computers and make up all these new stats can't make a stat for."