Entering 2012, the Braves had a pair of young rookies vying for the vacant shortstop position: Tyler Pastornicky and Andrelton Simmons. Both were good hitters in the minors, but Simmons proved to be ahead of Pastornicky defensively. Neither hit well in Spring Training, but Pastornicky was given the nod heading into the regular season while Simmons started the year at AA-Mississippi.
At the end of his first month of major-league action, Pastornicky was hitting .262 and was at .276 as late as May 21. The Braves would certainly take that out of the shortstop position, but what they couldn't take was his defense. Pastornicky committed seven errors at the shortstop position, many of them of the throwing variety. Couple that with his sudden struggles with the bat after his May 21 high point - 2 for his final 21 to end the month - and it was time for a change.
Enter Andrelton Simmons, and he didn't wait too long to have an impact. He debuted June 2 and recorded a three-hit game just two days later. He immediately proved to be an upgrade defensively while showing exceptional range: his Total Zone Runs of +16 was tops among all NL shortstops; that stands in stark contrast to Pastornicky's -11. Simmons' Range Factor/game of 4.59, had he qualified, would've also led the NL. He even proved to be a superior hitter: at June's finish, Simmons was hitting .333 with three home runs and 14 of his 19 RBI.
Simmons was rolling merrily along until July 8 when a headfirst slide into second base resulted in a broken right pinky finger. Veteran shortstop Jack Wilson filled in for all of two games before he was hurt with a dislocated finger. The team was hesitant to reinsert Pastornicky at shortstop, so Martin Prado filled in briefly until a trade was pulled off for Reds infielder Paul Janish.
Janish paid immediate dividends for the Braves on defense; it was as if Simmons was never injured. In 55 games, Janish only committed two errors and his +11 Total Zone Runs was second to Simmons among shortstops in the NL. His stellar play allowed Simmons as much time as necessary to heal his broken finger and more than made up for his .186 batting average.
After being recalled from Gwinnett when Simmons was injured, Pastornicky was restricted primarily to pinch-hitting duties - he was 4-20 in that role with a home run - while also serving as a pinch-runner. He started only two games after the All-Star Break, both at second base. Simmons returned to the lineup September 10 and hit .275 the rest of the season. Janish's season ended September 18 when he dislocated his left shoulder on the first play he made as a defensive replacement. Once Simmons and Janish appeared on the scene, Jack Wilson couldn't find any playing time and was ultimately released in August.
According to Baseball Reference, Pastornicky was so bad, his -1.5 WAR was better than just 10 other players and was the worst of all 2012 debuts. Simmons posted a more respectable 2.8 WAR, fourth among 2012 debuts.
Simmons still has some rough edges, but has all but assured himself the starting shortstop position in 2013. Pastornicky may be kept as a bench bat and utility player while Janish enters his first year of arbitration.