Since his debut in 2008, Jay Bruce has been one of the most consistent contributors to the Reds’ overall success. Through 2013, Bruce flashed incredible power, averaging a .225 ISO along with 2.7 fWAR. In 2014, however, Bruce had a negative impact on his team for the first time in his career, producing an fWAR of -1.1. While his knee surgery on May 5th could undoubtedly have contributed to his struggles the past season, that alone can’t explain the extreme drop-off in his production. There have been warning signs of multiple problems in the past couple of seasons; in 2014, these newly-acquired bad tendencies pushed Bruce past the tipping point and into a career-worst year.

Bruce had a massive power outage in 2014, generating a career-low ISO of .153, only 13 points above average. Even as a rookie, Bruce showed more power, as he posted an ISO of .199. His declining clout is the result of changes in approach, not the actual cause. There’s a difference between knowing that his power numbers decreased, and understanding the driving forces behind those struggles. The important question is, what were those changes?

Thanks to the efforts of Brooks Baseball and FanGraphs, we can pinpoint the reasons for his decline. The first piece of that answer comes via his swing tendencies, specifically his O-Swing% and Z-Swing%. In 2014, Bruce’s O-Swing% increased by 12.5% from 2013, while his Z-Swing% decreased by 8.8%. Both figures (O-Swing% of 33.4% and a Z-Swing% of 69.4%) represented the worst of his career, and were the dominant causes of his abysmal season. Seemingly out of nowhere, Bruce could no longer lay off pitches above the strike zone, or just off the inside.

With his increasing O-Swing%, Bruce’s O-Contact% also rose by 5.8%, causing his batted ball ratios to move in some unfavorable directions. His BABIP of .269 was the worst since 2009, which Bruce thinks may have been attributable to the increasing use of the shift. His O-Contact% also highlights an interesting point: Not all contact is created equal. While some may see the 5.8% increase as a good thing, since Bruce is making more contact by covering pitches that aren’t within the strike zone, that’s simply not the case. Some hitters (such as Pablo Sandoval) thrive by swinging at pitches they should have no business offering at, but Bruce is not one of those players. By making contact with more pitches out of the zone, his LD%, FB%, and GB% all suffered, as the dataviz below shows.

Another factor that undoubtedly contributed to Bruce’s decrease in production was his inability to hit the fastball. Throughout his career, he’s always been above-average in terms of pitch values, but once again, 2014 did not track with his history.

wFB wSL wCT wCB wCH wSF wKN 2008 5.1 -4 -0.4 1 2.2 -0.5 -0.8 2009 8.2 -3 -1 -1.7 1.4 2010 6.5 -2.8 2.7 4.4 4.7 1.5 2011 9.5 8.2 0.1 -3 2.5 -0.9 -0.4 2012 8.5 -1.1 -1.6 3 11.4 0.8 0.8 2013 19.6 -3.4 1.2 1.7 -0.5 0.3 2014 -3.2 -4.4 -1.5 1.8 -3.4 -0.1 0.7

For the first time in his career, Bruce was no longer above-average hitting against fastballs, and produced a negative value. This is extremely worrying, as Bruce should be in the prime of his career. It’s inexplicable that he’d suddenly lose the ability to do damage against a pitch that he’s historically demolished, especially considering how successful he was against it during 2013. However, it wasn’t just against fastballs that Bruce struggled. He’s had three consecutive years of regression against the slider, and two years for the change-up.

All of these factors led to Bruce posting just a wRC+ of 79, and an OPS+ of 84. While 2014 was clearly the worst season of his career, it’s something that may have been in the works for a few seasons now. His K% have increased every single season since 2009, while his walk rates have decreased since 2011. His wOBA and ISO have each fallen since 2012, and his GB/FB ratio has increased every season since 2011. With his inability to stay within the strike zone, and drive the ball deep, Bruce’s 2014 became a perfect storm for dramatic regression.

At only 28 years old, Bruce is nowhere near a lost cause, but that doesn’t make his 2014 season any less worrying. Heading into 2015, Bruce needs to make some adjustments in a hurry, and be sure he knows what pitches he can and can’t do damage against. If he continues to swing at pitches out of the zone, and make contact with them, then both his batted ball ratios and power numbers will continue to decline. It’s possible that in five years, Bruce’s 2014 season will look like an aberration, but for that to happen, he must make a strong and conscious effort to stop swinging at pitches that he can’t handle.

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

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