Buster Posey is an excellent baseball player. Since 2010, when he started accumulating regular playing time, he has been the 17th most productive player in the game. His career .308/.377/.388 and 140 wRC+ are very impressive. He has been an integral part of two championship teams and there is even a report that he is a good actor; it seems like the man can do no wrong. You likely already knew much of these Posey facts; however, this is all stated upfront because this article is going to be a bit nit-picky in looking at a slight weakness of Posey of which opposing pitchers may want to take advantage.
That weakness: hitting the slider.
Take as an example his plate appearance against Chris Perez in Sunday night's game against the Dodgers. This particular plate appearance is what developed my interest in looking into this idea. Here is a strike zone plot from the plate appearance (note that this is from the catcher's perspective and Posey is a right-handed hitter):
All four pitches that Perez threw were sliders. Only one of them was even close to the strike zone, but Posey swung at three of them. It was not pretty either.
Second swing (losing the bat!):
Now, obviously we do not want to make a huge deal out of one plate appearance. Looking deeper into Posey's offensive production as a function of pitch type reveals a relative difficulty with hitting sliders. Here are some relevant data for Posey's production off pitches seen at least 600 times:
|Pitch||Count||AVG||SLG||LD/BIP (%)||Whiff/Swing (%)|
Against the slider, Posey posts his lowest batting average, and line drive rate per ball in play, second lowest slugging percentage, and highest whiff rate per swing. It seems like the slider is a pretty good way to attack him. So is there evidence of opposing pitchers noticing this poorer performance and adjusting to throw more sliders to Posey? Not really. As shown in the table below, both right-handed and left-handed pitchers have been consistent with how often they throw Posey sliders:
There is a slight trend for pitchers to throw more sliders when they are ahead in count (~11%, ~22%, respectively for handedness), or have two-strikes (~17%, ~20%, respectively). But given Posey's suppressed performance against the slider, I am surprised that there has not been a trend to throw him more sliders, regardless of the count.
It should be noted that relative to himself, Posey struggles against the slider, but relative to all other players, he is essentially average. We can see this by looking at pitch type linear weights. These scores try to describe how batters do against each pitch type over the course of a season. If a batter hits a certain pitch really well, or really poorly, this will be evident. A score of zero is average, positive values are above average and negative values are below average. To correct for hitters seeing different numbers of each pitch, these scores can be standardized to a per-100 pitch rate with the range of scores typically falling between -1.5 and +1.5. Posey's career standardized score for sliders is 0.09 (ranking 108th for the years 2010-2014). So he is basically average against the slider, which is fine for the league, but for him, is poor.
Here are his values against other pitch types:
It seems as though opposing pitchers should throw Posey more sliders. However, caveats abound. Posey is a premier hitter and will make adjustments. In fact, last season was his first year with a positive pitch weight score for sliders (1.39). So these adjustments may already be underway. It is likely an interesting example of game theory. Posey is a clear offensive threat and my picking out this very small ‘flaw' in his performance provides additional support for this fact. He has produced MVP-like numbers even with this difficulty. Moreover, his performance from last year may suggest that he has already dealt with this issue and the plate appearance shown above was more about unfamiliarity with Perez than a general problem with hitting the slider. Either way, I am looking forward to seeing how this plays out this season.
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Chris Teeter is a featured writer at Beyond the Box Score. You can follow him on Twitter at @c_mcgeets.