The Low-Rider Grip
This is another common mistake amongst new shooters. This grip occurs when the webbing of the shooting hand doesn't get high enough on the backstrap of the grip frame of the handgun. In other words, there is space between the highest point of the backstrap and that sweet spot of your hand. Note that this mistake commonly appears in conjunction with other grip issues, but sometimes will occur even when the rest of the grip seems to be okay. The result of this incorrect grip is that we aren't using adequate leverage to provide sufficient resistance to the firearm's movement during recoil. We aren't high enough on the bore axis to maximize or our ability to keep that muzzle down during recoil which will negatively impact the amount of time it takes us to pick up that front sight and get our follow-up shots on target. While this will either further complicate other issues within the grip or be a stand-alone problem, it does prevent us from controlling the weapon as efficiently and effectively as possible. In short, your grip sucks. Fix it!
The Crossed Thumbs Grip
This grip is also a very common mistake with semi-automatic handgun shooters. It stems from the proper grip of a revolver. When gripping a revolver, a proper "thumbs forward" grip that is used on a semi-automatic would likely disrupt the function of the rotating cylinder. Therefore, the grip is modified by crossing the non-shooting thumb over the thumb on the shooting hand. On a revolver! When gripping a semi-automatic handgun, this presents a world of inefficiencies that will prevent you from performing as well as you could if you were utilizing a proper semi-automatic handgun grip. Usually these inefficiencies are in some combination of problems that other incorrect grips bring about. For starters, you are almost guaranteed to be too low on the grip frame, which means that you're suffering from the same problems that the Low-Rider Grip presents. Next, you're likely suffering from the same negative effects as the Tucked Thumb grip since it's impossible that you are making maximum contact with the grip frame when using the Crossed Thumbs Grip. Lastly, and perhaps most importantly, since you aren't utilizing a proper thumbs forward grip, you don't have your support hand locked out at the proper wrist angle which offers you the most control over the weapon's recoil. In short, your grip sucks. Fix it!
The Train Tracks Grip
This incorrect grip stands out as the "downright dangerous" grip that new shooters will sometimes use. This grip rears its ugly head when an inexperienced shooter crosses their support hand thumb behind the thumb of their shooting hand. Naturally, this also means that they have crossed their thumb behind the slide of the handgun. The slide that must cycle backwards in order for a semi-automatic handgun to function correctly. Thus we arrive at the reason for the name of this incorrect grip... When the slide cycles backwards, it will run over their support hand thumb that is crossed behind it. The result is a perfectly symmetrical set of bloody cuts where the slide's rails strike the crossed thumb. A cut is almost guaranteed, and a bruised or broken thumb is certainly not out of the question. This grip not only presents all kinds of inefficiencies to the fundamentals of shooting, but also likely presents injury to the shooter. It's unlikely that you'll make this mistake twice, but even so- your grip sucks. Fix it!
The Wrist Grab Grip
This incorrect grip is likely the most laughable. It looks silly, it provides virtually no perceivable advantages to the shooter, and I can't really think of a reason why this would ever be a good idea for a semi-automatic handgun grip. This is when the shooter will use their support hand to grasp the wrist of their shooting hand. To be brutually honest, I'm not sure where this grip came from, why it's still around, or who invented it. Perhaps the people who use this grip are huge fans of the 1950's mobster movies which frequently showcase this gem. Even when shooting a revolver- I'm not sure why one would choose to employ such a biometrically unstable grip. Personally, I would rather shoot one-handed than to utilize this grip. While I'm uncertain of its origins and possible advantages- it is common enough that I have seen quite a few inexperienced shooters using this incorrect grip. In short, your grip sucks. Fix it!
So How SHOULD It Be Done? See Below:
The Proper Grip of a Semi-Automatic Handgun