In 2011 the Braves had one of the game's better defensive shortstops in Alex Gonzalez. He was smooth, had an accurate arm, and almost never muffed anything. His range wasn't all-world caliber, but it was plenty good enough. When you combined Gonzalez, the aging Chipper Jones and a little bit of Dan Uggla, the Braves converted ground balls to the left-center of the infield at a pretty average clip, leading to a batting average on ground balls in play (henceforth GBBABIP) of .245 on the left-center portions of the infield (I will frequently use left-center infield in his article, what that precisely means is everything from behind the 2nd base bag to the third base line). That was good for 17th in MLB.
The right side of the infield, featuring Freddie Freeman and Dan Uggla was HORRIFIC in this regard, allowing a GBBABIP of .212, which was good for 28th in MLB. (if at first it seems weird that I'm calling a .245 good for the left-center, and .212 bad for the right side, remember that it's easier to turn a ground ball on the right side into an out, it being close to first base and all, this is why I gave their rankings as well).
Combining the average-ish left-center and horrific right sides of the infield, we saw the Braves allow a GBBABIP on the whole infield of .235, good for just 23rd in MLB. The Braves infield was not doing their pitchers very many favors in that season. It wasn't quite the Brooks Conrad level bad that had ended the Braves' season the year prior, but it was plenty bad.
In 2012, the Braves started the season with Tyler Pastornicky and used he and a grab bag of players at shortstop until Andrelton Simmons was called up on June 2nd of that year. To say the left-center infield defense was a disaster prior to Andrelton's arrival would be a drastic undersell. The Braves were allowing a .297 GBBABIP on the left center of the infield, which was the worst in MLB. When you ask "how bad does a defense have to be to be unworkable" that's pretty much your answer. A hitter, if he got to play that defense every day, may have literally been able to bunt his way to a batting crown. To be a winning MLB team, you CANNOT allow ground balls to the left side of the infield to produce .300 hitters. You simply can't win that way.
On June 2nd, 2012, Andrelton Simmons made his debut, a rookie attempting to patch the leakiest left-side infield defense in all of baseball. What happened? The Braves immediately became by far the best left side infield defense in all of baseball, allowing just a .220 GBBABIP on balls to the left-center of the infield for the rest of the season.
Let that sink in. We all intuitively know the difference between a .220 hitter and a .297 hitter is the difference between "can't make it in MLB" and "probable hall of famer." The previous players were turning average hitters into hall of fame caliber hitters, and Andrelton was taking average hitters and reducing them to "not good enough for MLB." But that's not really even the astounding part, because those numbers also included some time when Andrelton was injured.
Andrelton would actually suffer an injury from July 9th until September 9th, at which point the Braves turned to defensive specialists Paul Janish and Jack Wilson; the left center infield's GBBABIP during the time these two defensive specialists were replacing Andrelton? .256.
During the 54 games Andrelton Simmons was actually playing shortstop in 2012, the Braves allowed a left-center GBBABIP of .180, this sentence deserves its own bolded, italicized paragraph.
The Major league leader for the full season that year was the Washington Nationals, at .229. And again, remember that most of these numbers for Andrelton were with an aging, slowed Chipper Jones playing third base, who while he wasn't beyond belief awful, he certainly wasn't helping Andrelton out very much on the left side of the infield.
In 2012 Andrelton Simmons played 1/3 of the season, and in games he did not play the Atlanta Braves had the 3rd worst infield defense in baseball. The Braves finished 2012 with the 10th best infield defense in baseball. In only 1/3 of a season, Andrelton's glove allowed the Braves to pass 17 other clubs in turning ground balls into outs.
In 2013, we would see Andrelton Simmons for a full season for the first time. The right side had the same cast of characters in Dan Uggla and Freddie Freeman. While Dan probably got worse, Freddie probably got better. But Dan's decline certainly played the heavier role, as in 2012 the Braves held ground balls to the right side of the infield to a decent (10th in MLB) .173 GBBABIP. In 2013, the right side was more generous with the hits allowed, allowing a .203 GBBABIP (24th in MLB).
On the left side, we replaced the limited in range, but smooth enough Chipper Jones with a player who had a reputation amongst scouts as being the worst defensive third baseman in the league, Chris Johnson. While we were going to have Andrelton for a full season, it was unclear just how well these two would mix, because as good as Andrelton was, Chris Johnson might have been that bad, we just weren't sure.
The left-center infield defense did take a step back with Chris Johnson, all the way to .219, good for 2nd in all of MLB (the Pirates were best in MLB at .210). While that's still outstanding, it's a marked decline from the .180 the left-center combo of Andrelton and Chipper allowed when together in 2012. But Chris Johnson was an offensive force for the team, producing a .321/.358/.457 triple slash on the year.
Now, let's step into alternate reality for a second here. Let's assume (and it is an assumption) that the difference between the left side with Simmons in 2012 (.180) and the 2013 (.219) numbers was mostly attributable to the difference between Chipper and Chris Johnson defensively. Well, .250 is a roughly average left-center GBBABIP. And as we talked about in the open .290 is probably unworkable (side note: this was the Achilles heel of the Angels in 2013, they allowed a .289 GBBABIP on the left-center infield, explaining how you can be that bad and have Mike Trout). Well, if you consider that Chris Johnson probably cost us at least 40 points of GBBABIP, with an average shortstop, that probably means we can't play Chris Johnson at third base. In many ways, Andrelton Simmons is the entire reason why we could get away with Chris Johnson's glove at third. If we just have an average shortstop plus Chris Johnson, the defense is probably so lousy over there we not only miss the playoffs, but probably aren't close.
That's the beginning of the ultimate point I'll make about Andrelton Simmons. He should probably be the player you attempt to build your team around, because he's not just good. He's not even just great. He's transformationally, transcendently great at the most important defensive position in baseball. As a GM he allows you to get away with a multitude of sins. Can't afford ace, strikeout type pitchers? Well, if they can just get the batters to put the ball in play to the left side, Andrelton will convert those hits into outs at an unprecedented pace. Can't find a decent all around third baseman? That's fine, just find the best bat you can, and Andrelton will nearly literally cover half the infield. To those who've watched the Braves live, and compared infield positioning to other teams, this is not an exaggeration. No other third baseman played closer to the line than Chris Johnson. No other 2nd baseman made plays behind the bag less than Dan Uggla. Yet the Braves still had the 2nd best rate in all of baseball for converting those types of hits into outs.
Without Andrelton Simmons the Braves most likely would have had the worst overall infield defense in all of baseball in 2013, instead they had the 2nd best.
Andrelton gives Frank Wren options. He can build a powerhouse run prevention team if he'd like, by adding competent 2nd and 3rd base defensive players, or he can punt defense at those positions for offense and know the infield defense will still be exceptional (much like he did this year). While the Braves have other great young players in Freddie Freeman, Craig Kimbrel and Jason Heyward, none of them actually change the way you can go about building a team the way Andrelton Simmons does. Add in a developing bat, with some good pop, and we have the makings of perhaps the most valuable player in baseball in the years to come.