Heading into the 2015 season, Jered Weaver owned the fifth-lowest ground-ball rate (33.2%) among starting pitchers with at least 600 innings pitched this century. If you bumped that minimum up to 1250 IP, Weaver stood alone at the top. In no season of his career did his GB rate eclipse 36%, and he almost never induced more grounders than fly balls in any one game. Last year, for instance, he only twice got more batted balls on the ground than in the air, and he tallied double-digit ground balls in a game just four times in 34 starts.
This year things are different.
Not only has Weaver already matched his “more GBs than FBs” games from last year — in consecutive starts, no less — he’s also already tallied double-digit grounders five times, eclipsing his 2014 total in 23 fewer starts. As a result, his ground-ball rate this season has jumped a full eight percentage points1 from his previous two seasons, up to a career-high 40%.
When I first stumbled upon this little factoid last week, I thought that perhaps it could be simply explained away by Weaver’s increased reliance on off-speed pitches this season. He’s throwing more curve balls and change-ups than ever, so why wouldn’t his GB% go up?
If only it were that easy. Yes, Weaver’s ground-ball rate is up partly because of heavy use of his breaking stuff this season, but that doesn’t begin to explain why it’s at a career-high for every individual offering but his curve ball. Maybe a look at heat maps can help explain the change?
It looks like he’s throwing a higher percentage of pitches low down the heart of the plate, but that seems to be evened out by fewer in those lower left-hand boxes. If you add up all his offerings in the lower third of the strike zone and below for 2015, it comes out to 45.92% of his pitches. For 2013-2014, that total was 44.19%. While an increase of close to two percentage points isn’t totally insignificant, it’s also probably not big enough spike to give us the definitive answer for which we’re looking.
The next thing to do is look at the locations of all the balls put in play on the ground and compare it to the last few seasons. Is there a certain spot Weaver’s throwing to that has allowed him to nearly equal his 2014 GIDP total (7 vs. 9) in more than 140 fewer innings?
What stands out immediately to me is the big chunk of red in the three boxes at the very bottom left-hand corner of the 2015 chart, where 11 of 16 balls in play have been grounders. If you remember from the first chart, Weaver is actually throwing fewer pitches than ever in that location. That he’s also getting more grounders than ever in that spot seems to indicate that his being more selective in using that corner of the zone, primarily against LHHs, has made him more effective at inducing grounders there.
Juxtaposed against that spot are the three red boxes on the bottom right-hand corner of the chart, minus the corner itself. Weaver is going to these locations more than in years past but is seeing the same spike in grounders, with 20 of 30 balls in play thus far finding their way to the turf. Like the offerings in the other corner, these are mostly the result of RHHs expanding the zone and reaching for the ball.
Just why those pitches are turning into grounders rather than their usual pop-ups and fly balls is still something of a mystery, and probably comes down to the nebulous “pitchability.” Weaver has changed his pitch mix somewhat this season, trading sliders for curves early in the count against RHHs and four-seamers for change-ups late in the count against LHHs, so it’s possible that plays a part as well. Whatever the cause, it’s probably (maybe?) a good thing. More grounders will likely mean fewer opportunities for dingers, which were a huge issue for Weaver last year.
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1 The spike in grounders has pushed Weaver nearly out of the bottom 25 in terms of GB%, making way for another Angels starter to take the crown.
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