Carlos Martinez has rediscovered his nearly unhittable slider

Over his last three starts, Carlos Martinez has been nothing short of stellar. Allowing only one run in each start (1.29 ERA), Martinez totaled 21.0 innings pitched and compiled a season-high strikeout rate of 32.1%, all while keeping his walk rate below his career average (7.7% versus 8.6%). Of course, the Brewers (57-76) are one of the worst teams in baseball, but the other two starts came against clubs in contention for a playoff spot in their respective leagues (Astros and Mets). And using ZiPS rest-of-season projections as a guide (0.7 fWAR), Martinez is finally on pace to outperform his All-Star 2015 season (a year in which he posted 3.4 fWAR over 179.2 innings).

One of the main contributors to Martinez's success over his last three starts has been the reemergence of his "nearly unhittable" slider -- a pitch that, while still clearly successful (see table below), had been lagging slightly behind this season, by his standards (in 2015, the pitch yielded a .174 batting average and a .256 slugging), at least.

Results versus Martinez's slider

I am well aware of the extremely small sample size (65 pitches) we are dealing with here. Drawing conclusions from a total of 65 pitches is never recommended. Thus, I will not dwell on the fact that Martinez has not allowed a hit versus his slider over his last three starts. Or the fact that only four Martinez sliders have been put in play, with three of them being on the ground. Instead, based on some important PitchF/x-based findings, I will explain why I am thrilled with what I have seen out of Martinez's slider over his last three starts.

Martinez's slider location (via baseballsavant.mlb.com)

Location. Location. Location. For those who choose to fact check me, I must first note that BaseballSavant still classifies Martinez's breaking ball as a curveball because that is what the MLB GameDay algorithm spits out each time he throws the pitch. Thus, these heat maps were actually generated by doing a curveball search on Martinez's Statcast page. However, considering how few actual curveballs Martinez has thrown this season (13, per the manually classified, and much more accurate, BrooksBaseball), I feel confident in reporting the above heat maps as primarily slider heat maps.

With that disclaimer out of the way, the differences between the two heat maps are easy to spot. Over his first 22 starts, Martinez was unable to develop a true core location for his slider, as you can see by the appearance of two dark spots instead of the usual one. Now, when you look at a pitcher's fastball heat map, having two cores is not necessarily abnormal because a pitcher is going to throw it differently based on batter handedness, but when it comes to the slider, the location to attack is generally the same: down and away to righties or down and in to lefties.

Well, as you can see in the heat map on the right (his last three starts), Martinez appears to have found his groove in locating the slider. In fact, considering we are dealing with a much smaller sample size (67 versus 464), I would not have been surprised to have found a less defined (aka "looser") heat map, or one without a true core. That is what makes Martinez's slider location over his last three starts so impressive. Martinez has found a spot in the zone to attack and is hitting it consistently. Plus, this new core is closer to the edge of the plate (x: 0.5 versus x: 0.25) and is lower in the zone (y: 2.5 versus y: 2.75) -- both being desirable adjustments to his previous core location.

Martinez's slider data (via BrooksBaseball.net)

Remember: Regarding horizontal movement in right-handed pitchers, a negative value means arm-side movement, whereas a positive value means glove-side movement.

Location is not the only change associated with Martinez's slider, either. Just as we have seen with his fastball, it appears Martinez is dialing down the velocity on his slider as well. Because of the velocity decrease, he has been able to experience a slight increase in both horizontal and vertical movement. More movement is almost always a positive, just as long as there isn't a mechanical change causing it. Also, and I believe this to be an underrated point, but any deviation from his changeup velocity (86.03 MPH) should be welcomed because then it gives hitters at least three velocities to consider at the plate.

Bottom line

Martinez has been solid pretty much all season for the Cardinals. While his strikeouts are down, Ben Markham made the case that he has done a good job suppressing contact quality. If he is able to replicate the velocity, movement, and location of the slider we have seen over the last three starts, the Cardinals will be in good shape going into the stretch run. And should they make the one-game Wild Card playoff, you better believe who will be on the mound starting it.

And if you want to watch Martinez's 13 Milwaukee strikeouts in 13 seconds, MLB.com has you covered: