When Starlin Castro came up in 2010, he was a revelation, posting a 1.9 fWAR in his first 125 games at the big league level. The following season was even better. It looked like the Cubs had their solution at shortstop, but the next two seasons challenged that belief. His offensive numbers plummeted, and in 2013 he produced only a 0.1 fWAR, by far the worst of his career. Fortunately for Castro and the Cubs, 2014 was a different story, and he returned to being the valuable offensive player they used to know. Castro’s up and down career, and his propensity to lose focus, naturally lead to a question. Was 2014 another good season before an eventual downfall or the start of sustainable success?

Castro’s resurgence in 2014 stemmed from a major overhaul of his approach at the plate.

Castro has always had a tendency to swing at pitches off the plate high, low, and inside. In 2013, he added another troubling tendency--an inability to lay off pitches in the lower outside corner. The 2013 heat map shows how often he swung at those offerings, and as his swing rates rose, he was essentially inviting pitchers to attack that part of the zone. While his O-Swing% actually improved in 2013, (with his peak coming in 2012), his propensity to swing at pitches in the lower-outside part of the zone led to more issues. It wasn't until 2014 when he changed his batted ball distributions (discussed below) that his improvements were fully realized.

Year O-Swing% Z-Swing% Swing% O-Contact% Z-Contact% Contact% Zone% 2010 32.30% 64.90% 47.80% 75.30% 91.80% 85.90% 47.60% 2011 33.10% 67.50% 49.20% 71.20% 92.90% 85.10% 46.80% 2012 37.40% 64.90% 50.20% 71.20% 91.10% 83.10% 46.40% 2013 33.70% 65.00% 47.80% 70.50% 89.20% 82.00% 45.20% 2014 31.50% 65.00% 47.10% 67.20% 88.10% 80.60% 46.50%

His O-Swing% was the lowest of his career and represented a 15.8% decrease from 2012 and a 6.5% decrease from 2013. His Z-Swing% has always been incredibly consistent, varying only .1% over the last three seasons. In addition to his declining O-Swing%, Castro also significantly reduced the amount of contact he was making with pitches outside the strike zone, specifically by 4.7%. As I pointed out in my last piece on Jay Bruce, not all contact is created equal. With his O-Contact% decreasing, his BABIP rebounded to .337. While that number is significantly higher than MLB average, it’s not out of line with his 2010-2012 stretch and shouldn't be thought of as an anomaly.

As Castro struggled with outside pitches in 2012 and 2013, his batted ball ratios decayed.

<a href="#" mce_href="#"><img alt="Sheet 1 " src="https://public.tableau.com/static/images/St/StarlinCastro/Sheet1/1_rss.png" mce_src="https://public.tableau.com/static/images/St/StarlinCastro/Sheet1/1_rss.png" style="border: none" mce_style="border: none"></a>

From 2013 to 2014, Castro's LD% and FB% increased by 12.1% and 9.9% respectively, while his GB% decreased by 10.7%. These increases were likely influenced by Castro’s return to pulling the ball more. In 2014, Castro shifted his focus back toward left-center and less on taking the ball the other way.

With his changes in hitting approach and increases in LD% and FB%, Castro’s ISO bounced back. In 2014 he produced a value of .146, a .044-point improvement over his 2013 seasons. While an ISO of .146 is just a tick over MLB average, he's a shortstop, and a .044-point increase is still a great upgrade.

The last piece of Castro’s 2014 success was his ability to hit the fastball. In 2014, his pitch value against the fastball was an incredible 16.1. That value alone is enough to make hitting coaches smile, but when coupled with the knowledge that in 2012 and 2013, he posted pitch values of -3.6 and -8.5, it’s even more impressive. His improvement was not just restricted to the fastball however, as Castro also improved against the slider, cutter, and curveball.

In 2014, Castro was a changed man and posted the best offensive season of his career. His RE24 was 10.57 compared to -24.47 in the previous season. He also posted career bests in wRC+ (115) and wOBA (.341). Heading into 2015, all three of the major projection systems believe that Castro’s changes are sustainable. Steamer, ZiPS, and Baseball Prospectus are projecting him to be worth 2.3, 3.4, and 2.7 wins. With contention near, the Cubs can count on Castro to provide offense from the shortstop position and help take pressure off their young core of prospects.

. . .

All statistics courtesy of FanGraphs, Baseball Prospectus, Brooks Baseball and Baseball-Reference.

Matt Goldman is a Contributor to Beyond the Box Score. You can follow him on Twitter at @TheOriginalBull.