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Introducing STATS Advanced Heat Maps: Evaluating the 2018 MLB All-Star Game Starters

By: Stats Perform

Heat maps have been around the game of baseball for some time now. They’ve been used to summarize location for pitchers, and also to identify hot and cold zones for hitters. While the hitter-specific graphics can be enlightening, they usually don’t tell the whole story. Most of these graphics only contain data from pitches on balls in play.

Wouldn’t it be much more informative to analyze a heat map that assigns value to every pitch of an at-bat? Thanks to STATS, that’s now a reality.

Values are based on what the league-average hitter does with a corresponding pitch, factoring in location and type. The hitter receives a higher value if the result is better than the league-average result on an identical pitch. For example, making hard contact on corner fastballs or off-speed pitches below the zone generates a higher value. Hitters who lay off pitches just outside the zone get a higher value as well since those pitches are frequently chased by the league-average hitter.

Conversely, the hitter will receive a lower value if the result is worse than the league average on a corresponding pitch. For example, a hitter who takes a two-strike pitch down the middle produces one of the lowest values. The league-average hitter typically swings and makes hard contact on those pitches. However, laying off balls that are far out of the zone won’t move the meter much, considering the league-average hitter would typically do the same.

STATS has generated these heat maps to illustrate these values. For each player, red indicates positive value for that respective location and pitch type. The darker the red, the better a hitter is in that zone. Blue indicates the opposite; the darker the blue, the worse they are in that respective zone. So, if a player’s heat map is showing a lot of red on the outer edges, for example, that doesn’t necessarily mean that he is hammering pitches in that zone. With each pitch being considered, hitters can add value by laying off pitches out of the zone that the average hitter chases, thus showing red.

A player’s value-added in one zone also influences every other zone it touches, as well. In other words, when determining value for each hexagonal zone, the surrounding zones are also considered. This helps prevent sample size issues where a hitter may have only seen one pitch in a zone, but 23 pitches in a zone next to it.

Inversely, the lower the value, the better the pitch is from the pitcher’s perspective. For example, fastballs on the corners produce pitcher-friendly value because hitters often take them for strikes. When corner fastballs are actually put into play, it is with less damage than those pitches closer to the middle of the plate. In essence, pitches down the middle hurt a pitcher’s value because it’s where league-average hitters produce better results. In addition, breaking balls and off-speed pitches located below the zone are often chased at and missed, or they’re weakly put in play. These pitches produce a better value for pitchers. Pitches that aren’t close to the strike zone are typically taken by the league-average hitter. Therefore, they produce a poorer value for pitchers.

Note: Every heat map is shown from the pitcher’s perspective, not the catcher’s.

Now, let’s take a closer look at the National League’s starting third baseman in the All-Star Game, Colorado’s Nolan Arenado, who has been 27 percent better than the average hitter so far this season.

Arenado, a right-handed hitter, has struggled with pitches up and near the edge of the strike zone away. In the darkest blue zone, he has popped out 50 percent of the time, and the other 50 percent he has grounded out. Combined with the six zones surrounding it, Arenado has swung and missed 18.8 percent of the time, while league average in that area is 12.9 percent. His pop up percentage in that area is 32 percent, while average hitters are at 12 percent.

Arenado has also struggled up and inside, as shown on the map. His worst outcome of the season occurred on a 3-2 pitch just above the zone, which he swung at and missed. It would have been ball four if he would have taken the pitch.

In the highlighted zone above, Arenado has seen nine pitches and fouled seven of them off. His 78 percent swing rate in that zone compared to the 32 percent league average creates negative value, on top of the fact he has not done damage with any pitch in that location.

Arenado is an All-Star, and deservedly so, which means it’s not all bad for him on the map. Clearly, he crushes pitches low and in. In the area highlighted below, Arenado has been 303 percent better than the average hitter this season.

In that darkest red zone, he has an average exit velocity of 97 mph. League average is 89 mph. But looking at just that one zone doesn’t tell the whole story, considering each zone that touches it has an influence. In the seven highlighted locations, the average hitter has produced 3.13 runs this season, while Arenado has produced 9.5 runs. His swing-and-miss rate in that location is right around league average, so that doesn’t necessarily tip the scales, but his 11 home runs in those six adjoining zones certainly will.

Arenado has been one of the league’s best hitters to this point and is more than deserving of the fans voting him as an All-Star starter. Here’s a look at the STATS Heat Maps for the rest of this year’s All-Star Game starters.