I have been coaching baseball for 17 years and I don't think I have coached a game where an angry crowd didn't give the umpire grief over calling balls and strikes. Most of those games also had players showing disgust over balls and strikes called by an umpire.
Based on what I have seen over literally thousands of games (including watching countless MLB and other games on TV), I think most people (and even a lot of umpires) don't really know what the strike zone is.
In this post we will define the strike zone as per MLB and NFHS rules and give some examples of what is and isn't a strike and hopefully help some coaches, fans, and players gain a bit of perspective.
“The official strike zone is the area over home plate from the midpoint between a batter's shoulders and the top of the uniform pants -- when the batter is in his stance and prepared to swing at a pitched ball -- and a point just below the kneecap. In order to get a strike call, part of the ball must cross over part of home plate while in the aforementioned area.”
-- https://www.mlb.com/glossary/rules/strike-zone
Little League: NFHS rules are the same as MLB, but the Little League strike zone is a bit different. According to little Little League rules:
"the STRIKE ZONE is that space over home plate which is between the batter’s armpits and the top of the knees when the batter assumes a natural stance. The umpire shall determine the strike zone according to the batter’s usual stance when that batter swings at a pitch"
-- https://www.littleleague.org/university/articles/definition-little-league-strike-zone/
Softball is the same as little league, but other than this, the same principles apply.
The bottom of the strike zone is equally as arbitrary. Where is "a point just below the kneecap"? In the illustration above taken with a camera level with the ground you can see that the area of the kneecap is different for the front and rear kneecaps because of the stance of the batter.
There is also an issue of where is that vertical zone if the batter is "waggling" (to borrow a golf term). Some batters remain loose by bouncing up and down a bit as they wait for the ball to be pitched. Where is "in his stance and prepared to swing" if the batter is not standing still?
The answer to all of these questions is: it is wherever the umpire says it is based on his/her interpretation of the rule and it cannot be appealed.
There are some specifics, however about how the umpire should interpret the rule.
One important aspect of the strike zone as defined by MLB is, it does not say anything about where the ball passes the batter in the horizontal plane. By this I mean, the strike zone is not affected by the position of the batter within the batter's box - up or back in the box, crowding the plate, etc. It doesn't matter if the batter is in the front, middle, or back of the batter's box, the strike zone is defined by the location the ball as it crosses the plate and not where the ball passes the batter. Only the vertical aspect of the strike zone is affected by the batter and then only while in his/her stance and prepared to swing.
IMPORTANT: The term "prepared to swing" is important here. A good indication of when MLB considers the the batter to be "prepared to swing" can be seen while watching the strike zone box that the television broadcast puts on the screen when it is showing the pitch delivery.
Often, when the batter is standing in the batter's box waiting on the pitcher to begin the pitch, you will see the box looks like it goes from the belt to the bottom of the knees. However when the pitch is delivered and the batter begins his swing, he will bend his knees and couch down a bit as he starts to push off of his back foot and swing the bat. This bending of the knees results in the vertical size of the strike zone shrinking to the point that the box that started out at the belt is now midway between the shoulders and the top of the uniform pants. It is at this point that MLB considers the batter to be "prepared to swing".
NOTE: In many of the illustrations below the batter is in the box, but not "prepared to swing" as per the above definition. It is difficult to find usable pictures that depict a batter in the correct position with respect to the plate while in this position. It does not change the point being made in the illustration.
The average Major League fastball is dropping at about 6 degrees as it
crosses the plate, a curveball about 10 degrees. When a ball is only
traveling 60 MPH or less that trajectory will have a higher angle, but in youth league dimensions, the difference should be negligible. A 60MPH fastball on the typical 12U field is equivalent to a 90MPH fastball on a major league field. The images below use the MLB average for lack of a better reference.
Albert Pujols shows us a good position with respect to the plate where the ball is hittable anywhere in the strike zone.
Important: The black area around the plate is NOT a part of the strike zone. The definition of the strike zone above does not mention it, but the MLB and NFHS definitions of the home plate does not mention any black area and only talks about the white area. Further, the size of the plate is defined as 17" across the top border and a total of 17" deep with the angled area beginning at 8.5 inches from the front of the plate. If you measure the home plate at your local park you will find that adding the black area would make the plate too big.
Many times in youth league games a coach will tell a batter to move up or back in the box based on the speed of the pitches being thrown. The coach, player, and umpire should all be aware that this does not affect where the strike zone is.
The other aspect of the stroke zone is the inside/outside aspect.
Looking at the illustration to the left shows the difference in a ball and a strike with respect to inside and outside pitches. Both of these pitches are way too close to let go by with 2 strikes.
MLB pitchers can throw pitches which have been observed to break horizontally as far as 19 inches from release to crossing the plate. The average is 2 - 8 inches which brings the back of the plate into play - this is the case even for a middle school pitcher with a good breaking ball.
Furthermore, if a player's toes are on the edge of the batter's box, a pitch that catches the inside corner can feel like it is way inside even if it is a strike. Similarly, if a player is standing too far away from the plate, a ball thrown on the outside corner feels to the batter like it is way outside even though it is a strike.
For this reason, I coach my catchers to setup a player inside who is crowding the plate, and outside for a player who is way off the plate.
Both of the shown balls are too close to let go by with 2 strikes.
Now consider a ball that is thrown at the top of the strike zone and on the outside edge of the plate. With just a few millimeters being the difference in a ball and a strike on both the horizontal and vertical planes, whether a ball "catches the corner" or not is purely a judgement call on the part of the umpire. With no strikes, the batter will likely not get a good hit on such a pitch and if it gets called a strike the batter still has two more strikes to play with. With two strikes, though, there is no excuse for striking out if he/she doesn't put a swing on it.
In youth leagues, many umpires feel it is their obligation to "help young players grow" by calling any pitch that is close a strike to encourage batters to swing. In reality, these could go either way but a batter should always be prepared to be called out if they're looking at such a pitch with two strikes.
Finally, considering what has been discussed here and the tiny differences in a ball or a strike, perhaps showing a young umpire some grace on those pitches "on the corner" is the proper thing to do.
