Matt Kemp’s Fastball Struggles Revisited

A few months ago, I posted in the Community Research Blog on Matt Kemp‘s struggles against fastballs this past season, highlighting how he whiffed on more fastballs in 2010 compared to that of 2009, particularly high fastballs as well as fastballs down the middle of the plate. I showed that he displayed a lower contact percentage on fastballs down the middle in 2010 as opposed to 2009, and I posited that, since his whiffing behavior was season-long, his 2010 offensive struggles may have been due to a change in swinging mechanics, or worse, a season-long injury kept hidden from the media.

In light of the Kemp/Rihanna breakup, I thought I’d take another look at Kemp’s 2010 offensive struggles again (he struggled in the outfield too, but that’s for another day). As a recap, Kemp went from .297/.352/.490 in 2009 to .249/.310/.450 in 2010, highlighted by an increase in strikeout rate from 22.9% to 28.2%. Some of that was due to struggles against fastballs. Take a look at Kemp’s swinging strike percentage (per pitch as opposed to per swing) against fastball height (I looked at only four-seam fastballs):

The lines represent the top (right on the graph) and bottom (left) of the rulebook strike zone while the grey line shows the league average. In 2009, Kemp whiffed on slightly more fastballs than the average hitter no matter the pitch height. But in 2010, Kemp swung and missed at many more fastballs, particularly high fastballs in the zone. Here’s a look at Kemp’s contact percentage per pitch against fastball height:

This shows how the 2009 Kemp made what appears to be more solid contact on high fastballs in the zone while maintaining a league average contact percentage on down-the-middle and low fastballs. However, the 2010 Kemp dropped below average in making contact against fastballs that were located within the strike zone.

So it looks like Kemp has not been able to catch up with high fastballs, the type of pitches he used to crush before. I was curious to see how Kemp performed differently based on a fastball’s speed. Here’s Kemp’s swinging strike percentage against fastball speed:

95+ mph fastballs resulted in similar whiffing behavior, but Kemp’s whiffs against lower-90s fastballs dramatically increased in the past year, nearly doubling that of the average hitter. It’s not that Kemp is missing a lot of plus-plus heat — he’s consistently whiffed on 20% of 98 mph fastballs throughout his career. He’s missing average fastball speeds as well. Finally, let’s look at Kemp’s contact percentage against fastball speed:

Similarly, Kemp’s contact percentage curve is completely submerged below both his 2009 contact percentage curve and the league average curve. He’s actually made less contact on 90-92 mph fastballs than on mid-90s fastballs, though I wouldn’t read too much into that without knowing the sample by pitch speed. (On a side note, it’s interesting to see how contact percentage is not particularly dependent on fastball speed on average, but this graph ignores fastball movement and the solidity of contact made.)

A quick look at Kemp’s plate discipline statistics tells us that Kemp actually swung the bat less in 2010 compared to 2009, so his high swinging strike percentages regardless of the location and speed of the opposing fastball are not overstated (here’s Kemp’s swing percentage against fastball height and fastball speed).

In the most recent Hardball Times Baseball Annual, Jeremy Greenhouse’s excellent piece titled “Scouting by Numbers” found that “pitchers cannot survive throwing 90 mph fastballs up in the zone.” In 2010, those pitchers did not have to worry about Matthew Ryan Kemp. Kemp is going to have a long season in 2011 if he doesn’t figure out how to perform better against low-90s and/or high fastballs the way he used to. Either that or he’ll have to get over Rihanna.

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Albert Lyu (@thinkbluecrew, LinkedIn) is a graduate student at the Georgia Institute of Technology, but will always root for his beloved Northwestern Wildcats. Feel free to email him with any comments or suggestions.

11 Responses to “Matt Kemp’s Fastball Struggles Revisited”

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  1. Scout Finch says:

    Nice work! May the NL West exploit this information. Perhaps they already have.

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    • Travis says:


      Albert, would it be possible to look at the rates of fastballs thrown per plate appearance against similar components (height and velocity)? I’d be very curious to see if teams started throwing him more fastballs as the season went on.

      This is probably a bit ahead of ourselves, because some base research would need to be done about the basic data on overall at-bat pitch selection trends, from both a hitter’s and a pitcher’s perspective. But it could be very interesting to have data reflecting the league’s adjustment against particular guys…

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  2. CJ says:

    I’m wondering how similar graphs would look for Jeff Francoeur, although I suspect it will just make the KC fans sadder and do nothing else, since neither the French or the KC management will care..

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  3. Jimbo says:

    Most interesting one is the Swinging Strike by speed. My theory: he saw more offspeed pitches in 2010 vs 2009, so perhaps he didn’t make adjustments to pitcher adjustments.

    As for the upper end of the speed readings, how many guys throw 96-98? Not the majority. If you see Brian Wilson in the 9th, odds are you’re geared up for his heat…since odds are good that is what’s coming.

    22 relievers averaged a fastball at or above 95 mph last year. Only two starters can say the same.

    Question is, what does he do next year? Is there reason to believe he’ll bounce back? I see his Avg, OBP, and SLG all trended down as 2010 progressed. His BB% and K% were pretty flat–offering me little other than hope to base an early draft pick on.

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  4. Dusto says:

    I like the argument that he was seeing more offspeed stuff and looking for it when he would get beat by a fastball.

    Is there a possibility that he simply needs to get an eye exam?

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  5. RZ says:

    pitch height would be better on the y-axis but neat graphs otherwise.

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  6. phoenix2042 says:

    can we see some graphs on how he fared against offspeed pitches? if he was laying off fastballs he could no longer hit and focusing on the breaking stuff, did he compensate and perform better against curves and sliders and changes? it would go a long way towards explaining his weakness to the fastball if he is in fact waiting on offspeed pitches now.

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  7. Dudley says:

    I’m afraid this looks like another example of Mr. Liu’s failure to appreciate the concepts of sample size and statistical significance. Kemp actually graded out as 5.7 runs above avg on fastballs in 2010, which isn’t too far off from his career numbers. Moreover, he had an even lower fastball score in 2008, when he hit .290/.340/.459.

    Kemp’s real problem appears to be that he got fat and slow. His speed score fell from 7 to 5.5, his fielding plummeted from +3 to -24, and his infield hit % went down from 12.1% to 5.6%. This leads me to think his 60 pt drop in BABIP had as much to do with pathetic base running, as it did bad luck.

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  8. Alex says:


    Any thoughts as to the causes of the big drop from 09 to 10 that you illustrate in these graphs? Any thoughts as to how / if he’ll bounce back in 11?

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