There are many causes of forearm tightness and one of the first things to investigate is a possible error in wrist mechanics.
To clarify some language: put your hand in front of you with the palm up and wrist straight. This is the wrist in extension, the normal or at resting/neutral position of the wrist.
If you bend your wrist bringing the fingers toward the forearm, this is flexion.
If you bend your wrist fully in the opposite direction, this is hyperextension.
Hyperextension of the wrist, seen less frequently, is also an error that can create huge problems for the arm, because it is usually accompanied by hyperextension of the elbow (an elbow that straightens too much).
Both of these flaws are unwanted actions at the wrist and can create tightness in the forearm, major fatigue especially as the innings progress, and can eventually lead to elbow and ulnar collateral ligament (UCL) problems.
To experience hooking and hyperextension: take a four-seam grip on the baseball and notice that the correct wrist position is in a slightly greater angle of extension (toward hyperextension) but not so much that you feel any activity in the forearm. Go through both incorrect angles of flexion and hyperextension and notice the unnecessary and unwanted activity in the forearm.
If you suspect a wrist problem with one of your pitchers, make sure your start by observing his wrist position inside the glove.
Then, track the ball down to its lowest point after hand break, and watch the wrist action as the ball is being raised to the early cocking position. (High-speed video is very helpful!) Most errors occur during this initial phase of the motion.
Once you see exactly the point at which the wrist loses its stabilization, have the pitcher do dry drills of starting in the glove and going to the problem moment and concentrating on eliminating the unwanted action.
As most of my followers know, I am passionate about the topic of forearm health. If you are a coach and think you have a pitcher in trouble with this issue, please feel free to contact me if you need further clarification. Forearm issues are one of the top risk factors for UCL problems so let’s work together to nip this one in the bud.