I don’t think over fretting is a commonly used term, but what it essentially means is: Pushing strings harder than necessary on fretted instruments.
We see several issues arise from pushing strings to the frets harder than necessary.
Tuning Distortion
Pushing a string to the upper back edge of a fret is all that is needed for good tone. Pushing a string down till it touches the fingerboard can stretch the string over the fret further than necessary and make the note sharp. Pushing the string down harder than necessary will sharp the pitch of the notes you fret.
Accelerated Fret Wear
Too much pressure will accelerate fret wear. Traditional frets are made of nickel silver. This is a soft, easy to install metal that is great to work with for repairmen and luthiers. If the right grip pressure is used, nickel silver frets last for years of regular playing.
Fingerboard Gouging
When the string is pressed beyond the upper back edge of the fret, all the way to the surface of the finger board, the combination of steel string and possibly the finger nails of the player can literally gouge the finger board surface. Techniques like “Choking” the string or “bending notes” where the steel string is rubbed across the wood accelerates this wear.
The Cause
The ideal way to fret a string is to push it only to the upper back edge of the fret. Pushing the string further toward the fingerboard surface “stretches the string” and makes the note sharp.
This is especially true of banjos that have relatively tall frets. The reason for tall frets is improved playability. The taller a fret is, the less effort it takes to push the string to the upper back edge of it.
Many old banjos from the early to mid-1900s have shallow, skinny frets and they require a greater gripping force to create a clean, clear note. Players who grew up playing these old banjos almost always grip new Deering banjos too tightly and distort the tuning, making the notes sharp.
Steel string guitarists and mandolin players have a very strong fretting grip because of the string tension on their instruments. Often when these musician’s pick up a banjo, they push the lighter string harder than necessary and often complain about notes going sharp.
It is easier to play faster and with less effort with the taller frets Deering uses. Why?
Since you only have to push the string to the upper back edge of the fret, it takes much less effort to hold a string for a clear note. This is why taller frets are “faster”. You don’t need to “grip like iron” to get a clear tone, you can “touch” the string to the fret instead of “grip” the string to the fret.
This is one of the reasons Goodtime, Deering, and Vega banjos play so comfortably.
The Solution
Most problems with sharp notes due to over fretting are on the 3rd string and to some lesser extent the fourth and second string.
The best training technique to eliminate this is:
Fret the string the way you usually do. Use the third string as it is usually the most problematic for grip tuning problems.
While fretting the third string, pluck the third string only with your fretting hand continually and regularly.
Very slowly, decrease the pressure you are using to hold the string to the fret until the string sounds like a “thump” instead of a note.
Now, very, very slowly, increase the pressure you are using to hold the string ever so slightly JUST until the string sounds clear.
Once the string sounds clear and is not sharp, pluck that string ten times with your picking hand, while keeping your mind on using “just enough” pressure to keep the note clear.
Now, take your hands off the banjo completely and rest for about one minute.
Repeat this exercise.
Repeat this fretting and resting exercise about five times.
Once you do this simple technique, you will find that your finger automatically presses the string with less pressure. The more you practice this, the sooner you will “touch” the strings instead of “grip” them.
The lighter your fretting pressure, the faster you can change chords and move your fretting fingers because you are not slowing yourself down by “gripping too hard” or “over fretting”.
Remember, it’s faster to toss a tennis ball from your left hand to your right hand than a 16 lb bowling ball. It’s faster therefore to move your fingers across the fingerboard when you are “touching” the string to the fret and not “gripping” the string to the fret.
Also remember, don’t “think to the fingerboard.” “Think to the fret”. In other words, focus on just getting the string just to the back edge of the fret and no further.
It’s ok to touch the fingerboard, but you don’t want to “think to the fingerboard” and you don’t have to grind the string into it.
Tall & Light is Just Right
So, “think to the fret” and “just enough pressure”.
Anything more will make you needlessly work harder and slow you down.