In this post, we’re going to walk through how to evaluate a hitter’s plate discipline based on stats and in-person/broadcast looks.

If you prefer video walkthroughs, check out this video:

What is Plate Discipline?

Plate Discipline describes the decision-making process at the plate. It evaluates a hitter’s ability to swing at pitches that he can do damage on, and to take pitches he can’t.

How to Evaluate Plate Discipline Using Stats

We are essentially trying to figure out how good the hitter is at deciding when to swing and when to take a pitch. There are some stats that can help us get an overall sense of a hitter’s plate discipline:

1. Walk Rate: This is the highest-level plate discipline stat. Can the hitter work the count and walk? MLB average walk rate is 8%, so the higher the better.
2. Zone Swing Rate (Baseball Savant): How often does a hitter swing on a pitch that is thrown in-zone? The higher zone rate the better, but do not make any conclusions just based on a high zone swing rate. Some hitters have aggressive approaches and swing at everything. We want to find hitters who swing at pitches in-zone and limit chasing.
3. Chase Rate (Baseball Savant): How often does a hitter swing at a pitch out of zone? The lower the better, but do not make any conclusions just based on a low chase rate. Some hitters have very patient approaches, and do not swing that often. We want to find hitters who do not chase, but also swing a lot against pitches thrown in-zone.
4. First pitch Swing Rate (Baseball Savant): How often does a hitter swing first pitch? If this number deviates significantly from average, we can get a high level understanding of their plate approach (are they more aggressive early in the count, or do they like to watch a couple of pitches?). Aggressiveness and patience are both neither good nor bad, it depends on what works best for that particular hitter.

Note: When we talk about plate discipline, we are not talking about bat to ball skills (strikeout or contact rates). The ability of a hitter to make contact with the ball is a separate skill to how he controls the zone. For example, I would consider Joey Gallo (a three true outcomes hitter) to have above average plate discipline, but also poor bat to ball skills. He has excellent walk rates, swings in-zone more than average, and chases less than average, but his strikeout and contact rates are poor.

Stats Aren’t Enough to Evaluate Plate Discipline

While stats definitely give us a solid foundation for a hitter’s plate discipline by identifying long-term trends, they do not tell the full story. Here are some things to watch for during games that can supplement the stats:

1. Game situation: Is the hitter swinging or taking pitches at an appropriate time when considering the game state? For example, if a pitcher clearly has no control and walked two batters, is the hitter swinging at the first pitch?
2. Swinging at Clear Balls: Is the hitter consistently swinging at pitches that land over a foot outside the strike zone and/or look like they are balls coming out of the pitcher’s hand? While chase rate let’s us know how often a hitter chases, we don’t know where the ball was they chased. It is a lot different to chase a pitch right off the edge of the zone than it is to swing at a ball two feet outside.
3. Limitations of Chase Rate: Chase rate includes balls that are one inch off the plate. If a hitter is swinging at those pitches, especially in counts with two strikes, I would not hold that against him.
4. Thinking About What’s Coming: Does the hitter look like he is thinking about the pitch sequencing, or does he look lost? For example, is the hitter chasing and then letting a fastball go right down the middle? Is his timing consistently way off? For this one, be careful. If the hitter is facing a good pitcher, take this with a grain of salt. But if everyone is seeing the pitcher well except one hitter, its something to consider. There are also many other factors that could be playing into occasional poor decisions, so don’t form a concrete decision after one game.