1. That fastball wasn't a regular Kershaw fastball
A typical Kershaw fastball comes out of his hand at 93.836 mph, but because he's releasing the ball at an average extension of 6.547 feet in front of the rubber, the "perceived velocity" -- or what it looks like to the batter -- is actually 94.178 mph. Though he's not necessarily an elite flamethrower, that improvement is still quite good; among pitchers who have thrown the four-seamer at least 40 times, his velocity ranks 110th, but his perceived velocity is 87th.
On that pitch, however, the output just wasn't what you'd expect. This one came out of his hand at only 91.614 mph, and because he didn't get as much extension as he usually does -- only 6.075 feet -- the perceived velocity was only 90.909 mph. A usual Kershaw fastball seems faster to the batter; this one actually looked slower. Toss in the fact that his usual fastball spin rate is 2230.421 rpm, and this one was at just 2135.124, and it's clear to see that this wasn't a typical Kershaw offering.
Now, that might not have been an issue, except …
2. The placement couldn't have been worse
If we watch the video, we can see where Kershaw put this pitch, and, well, this is why they say a picture says a thousand words.
A standard-issue Kershaw heater can get away with being down the middle. A flat Kershaw fastball down and away might not be remembered. But a sub-par fastball right down the middle of the plate, well, even he can't get away with that.
Worse, the pitch came at the exact moment when hitters know they ought to be attacking him …
3. It came on the first pitch
Over the last few years, hitters have learned that getting down two strikes against Kershaw, when he can bury them with that slider or curveball, is a recipe for disaster. In 2010, hitters offered at just 6.489% of Kershaw's first pitches, only the 98th-highest rate in baseball. Last year? 11.131%, the highest rate in baseball. To restate that: No pitcher in baseball in 2014 saw as many swings on 0-0 counts as Kershaw. And why not? 85% of his first pitches last year were fastballs. At least you've got a prayer against that, as opposed to that 1-2 slider.
Though first-pitch swings haven't increased against him this year (down slightly to 10.276%), the productivity has continued, with a .400/.400/.743 first-pitch line headed into Thursday's game. When Kershaw is ahead in the count, that falls to .203/.214/.333. When he has two strikes, it's .144/.226/.250, which is a numerical version of saying "don't even bother."
The rumors of Kershaw's demise, it must be said, are sorely exaggerated: His 2.88 FIP -- a metric on the ERA scale that focuses on events the pitcher has complete control over and strips away things like defense and "luck" -- is far more representative of his performance than his 4.32 ERA. Even so, the best pitcher on earth can't get away with a first-pitch meatball right down the middle, even when the other pitcher is batting.