Should We Worry About Matt Wieters's Plate Discipline?

All data as of Thursday, August 20th.

Matt Wieters has had a pretty volatile career with the bat. After displaying seemingly limitless potential in the minors, he stumbled out of the gate, posting an 89 wRC+ across 2009 and 2010. Two prosperous years (110 and 107 wRC+) followed that, but the hardship of 2013, when he plummeted to 87, didn't give much hope for the future. Then came 2014, when he smashed his way to an abbreviated 134 wRC+. Thus far in 2015, he's sustained some of that success, with a mark of 106 in his 171 trips to the plate. As he prepares to hit the free agent market in the offseason, prospective teams may want to note the unnerving occurrence that has impacted his performance.

Wieters has always made pretty good contact, regularly possessing hard-hit rates above the MLB average, and 2015 has not seen him change significantly in that regard. Moreover, he's popped the ball up a lot less than ever before, and his line-drive rate has spiked. He therefore seems to have earned his current .167 ISO and .347 BABIP; unless his hamstring injury hamstrings limits him, those should remain high.

Something has regressed for him, though. He always used to limit his strikeouts and accrue a good amount of walks, but that hasn't held true for 2015:

Season	uBB%	uBB%+	K%	K%+
2009	6.8%	82	22.3%	124
2010	8.1%	102	18.7%	101
2011	8.2%	110	15.2%	82
2012	9.5%	128	18.9%	96
2013	6.6%	89	18.0%	90
2014	5.4%	75	17.0%	83
2015	4.2%	59	24.6%	118

As Wieters ages, he'll need to rely more and more on these skills, so their sudden deterioration doesn't bode well for the future. Let's look through his peripherals to decipher the source of his struggles.

Wieters has always swung at a fair amount of pitches outside the strike some, with a career O-Swing% of 31.6%. Perhaps uncoincidentally, pitchers facing him have generally avoided the zone, throwing 46.0% of their pitches there. Those trends haven't moved much in 2015 — Wieters owns an identical 31.6% O-Swing%, along with a marginally-higher 46.6% Zone%. If Wieters hasn't declined in these regards, something else must be behind his depressed walk rate.

His counterparts behind the dish haven't done him any favors. 64.4% of the pitches he's seen this year have gone for strikes, compared to 62.8% for his career and 63.4% based on the aforementioned PITCHf/x data. Should he stick to his approach, this will come down as he compiles more opportunities against poorer backstops. But this can't account for the massive drop he's undergone.

Earlier this year, I examined Manny Machado's situational aggression. Like (I assume) most hitters, he's always swung at more pitches when the ball count inches near four. Although Wieters has always trended similarly, he's taken that to a new extreme this season:

2009-2014	O-Swing%	Zone%	xStr%	2015	O-Swing%	Zone%	xStr%
0 Balls	25.4%	34.7%	51.2%	0 Balls	27.6%	32.8%	51.4%
1 Ball	38.2%	34.6%	59.6%	1 Ball	40.7%	33.0%	60.3%
2 Balls	43.6%	38.5%	65.3%	2 Balls	50.7%	41.8%	71.3%
3 Balls	47.6%	50.3%	73.9%	3 Balls	63.6%	56.9%	84.3%

After two balls, Wieters's theoretical strike rate has spiked, to a significantly greater degree than it used to. This means that, while he's retained his patience during the earlier part of at-bats, he's ditched it thereafter. The effects of this become clear when we look at his ability to capitalize on three-ball counts:

Year(s)	PA	3-Ball PA	3-Ball PA%	BB	BB/3-Ball PA
2009-2014	2701	563	20.8%	211	37.5%
2015	171	34	19.9%	7	20.6%

He's made it to the brink of a free pass to a slightly lesser degree than he did in years past, but he hasn't taken nearly as many fourth balls, confirming the shift from his count-based swing marks. Maybe Wieters feels that he must chase more pitches in these situations, to fend off the effects of aging on his power. In any event, sustaining this pattern would keep his walk rates in the Jones range.

A decline in walk rate doesn't necessarily portend offensive inadequacy, as it can also accompany a lower strikeout clip. Wieters obviously hasn't benefited from that: His present 76.9% contact rate (down from 80.7% for his career) gives him a bloated 11.2% swinging strike rate, erasing any memory of his 9.0% overall mark and bringing up his 2015 strikeout rate.

The most common type of pitch has given Wieters the most trouble:

Year(s)	Hard	Breaking	Offspeed
2009-2014	7.2%	14.7%	13.6%
2015	10.0%	15.5%	12.5%

At the same time that his whiff rates have stayed about the same against breaking and offspeed offerings, Wieters has swung and missed a ton more at the hard stuff. Because they comprise about 60% of the pitches he encounters, this explains virtually all of the rise in his swinging strike rate.

Based on the fastball location against him, we can see why this has occurred. High heat has always confounded Wieters:

That's stayed the same thus far, so it makes sense that pitchers would target it:

Wieters has yet to cover up this hole in his swing, and if that remains the case, he'll continue to go down on strikes at a high level. The game is all about adjustments, which he has yet to make.

Wieters will almost certainly never fulfill the potential that many deemed he could. If these developments in his offensive profile stick around, his bat might fall even shorter of that potential than ever before. With as many free agents as the Orioles will have this offseason, they may want to look elsewhere for their rotation's next battery mate.