When a hitter swings and misses and timing is right, almost always this is a result of swinging under the ball.
Here is an excerpt from my book The Ultimate Hitting Training Guide (available on Amazon):
The TOP TEN REASONS HITTERS SWING UNDER THE BALL:
#1 (By Far) - Faster and More Level Pitching
There are two concerns when developing hitters bump up in the level of play and face faster pitching. The first is very apparent. Since pitching speed is faster and the ball arrives sooner, the hitter adjusts timing to compensate. Practice drills in Tool XXV: Universal Timing of Fastball Drills.
The second concern is usually more impactful. The faster pitch arrives at the plate at less of a downward trajectory than the slower. A more level pitch, not late timing, is the primary reason hitters strike out when facing faster pitching. Typically, the entire team is consistently swinging under the pitcher with better than the average velocity.
It is useful to recognize how the brain establishes patterns. To bring the bat into contact with a flying ball, the brain sends thousands of impulses to muscles in a matter of milliseconds. Automatic patterning is mandatory - thinking is too slow.
Generally, developing hitters are accustomed to the steeper downward angle of the slower pitching speed they face in practice. When the pitch comes in faster and more level, the brain must establish a new pattern since the old model assumes a more downward trajectory; the mind must be taught how to bring the barrel into contact with the more level pitch.
Here is an analogy that might help training. Imagine the brain as a cornfield. There is only one path through the cornfield for most developing hitters. While this path is vast and well-worn, it is for one trajectory of pitch. There is no path for more level (or more dropping) than average pitching speeds.
A re-patterning training plan shortcuts the process of training the brain, more quickly creating a new path in the cornfield. The hitter dedicates four practices to pitching speeds at least five mph faster than average game speed. Crucially, there is no need to force a mechanical swing change. And generally, unless the hitter is “dipping” or “hitching,” there is no need to get hands higher.
The hitter swings with their baseline swing but aims the barrel higher.
To avoid a frustrating practice of swinging under every faster and more level pitch, especially pitches up in the zone, the hitter “teaches their brain” by focusing on:
Aiming their swing slightly over the ball or at the top edge of the ball. Aiming over the ball is very difficult to do at first. Mentally overriding any strong pattern is challenging. The hitter internally controls the vertical barrel height, striving to swing over the ball to hit the middle of the ball.
Hitting ground balls by aiming higher, not by chopping down on the ball.
Re-patterning is complete when the hitter can resume aiming at the middle of the ball, and line drives result. Re-patterning for faster pitching can be a long process if the hitter’s practice routine continues to include repetitious slow tosses, machine, or BP. Creating and maintaining a “new path through the cornfield” requires walking that path regularly.
The hitter only creates new pathways in the cornfield by frequently “walking that path.”
#2 – “Dipping”
Often, developing hitters drop the rear shoulder below the front shoulder before hitting position is reached. “Dipping” is a consequence of tee ball and slow, dropping pitches in the early years. The hitter’s barrel habitually “dips” too low then uppercuts. Then, as pitching speeds increase, dipping results in frequently swinging under, especially for waist high and above pitch locations. Purposefully practice Philosopher Lesson VII: Fix Dipping.
#3 – High Pitch
Hitters struggle with chasing the high fastball above the zone or swinging under the high strike throughout their playing careers. Through deliberate training, hitters can minimize the times they chase high non-strikes, swing under, or hit the bottom of the ball. Practice Tool XXVIII: Pitch Location Drills, Drill VI – High Pitch Drill.
#4 – Lunging
When the hitter’s head moves more than four inches past the center of their feet, towards their front foot, they create a downward swing plane, often resulting in swinging under the ball.
Practice drills Tool XI: Universal Stride and Approach Drills, Drill VI – Head Centered Drill, and Tool XVI: Universal Core Drills, Drill IV – Axis of Rotation (Stay Back) Drill.
#5 – “Pulling” Head
A stable spine angle during rotation is critical for vision, balance, and a consistent swing plane. When spine angle decreases, the hitter’s shoulders move away from the plate. The barrel path typically redirects below the ball slightly. Popups and missing under are more frequent for the hitter who consistently becomes more upright in their posture (pulls head) during swing execution. Practice Tool XVI: Universal Core Drills, Drill III – Stable Spine Angle Drill.
#6 – Hitching
Another common cause of swinging under is created by hitching hands to a point below the top of the strike zone. The habit of hitching occurs during the stride and separate (load hands) swing phase. Low hands at launch is a serious obstacle to productivity for pitches up in the zone. The hitter is unable to get on plane with the high pitch when their hands begin too low. Frequent misses under and fly balls are symptoms. Practice Philosopher Lesson IV: Fix Hitching.
#7 – “Rusty”
During the new season's first hitting practice, hitters are often swinging under the ball - a rusty hitter typically swings under the ball. Hand-eye coordination can also become rusty later in the season when:
• Hitting practices are insufficient in frequency and quality.
• The hitter consistently sees a slower speed and more dropping trajectory during practice than during games.
Practice Tool III: Hand-Eye Coordination Drills.
#8 – Undeveloped Lower Body Mechanics
Due to undeveloped lower body techniques, the head and shoulders may drop as the swing executes. A lowering head is especially prevalent for developing hitters with more aggressive strides. The big strider must avoid getting too broad with their feet, causing the torso and head to drop substantially—train un-weighting the rear foot and dragging the rear toe forward a few inches before contact. From the pitcher’s view, the coach can pin the hitter’s head to a background and help the hitter practice their approach. The hitter’s head stays steady as viewed from the front. Practice Tool XIV: Universal Leg Drills.
#9 – Rise Ball (Fastpitch Softball Only)
At about age 14, some fastpitch softball pitchers have gained enough velocity to throw an effective rise ball. The fastpitch hitter makes adjustments to avoid a drop in productivity. Practice drills Tool XXX: Movement Drills, Drill III – Rise Ball Drill, and Tool XXXI: Mental Training Drills, Drill VI – Rise Ball Plate Approach Drill.
#10 – Adjustments to Attack Angle
When hitters initially make a significant attack angle (swing plane) change, it is common to see timing and barrel precision issues when facing game speed pitches. The best way to work through this initial discomfort is purposeful swings off a tee and front toss conducted between machine and live pitch sessions at game speed. The hitter needs to see game speed so they can practice applying the new positions and movements.