Grip tightness

Think of keeping your grip relaxed.  You can add a little pressure for faster shots.

Your grip will naturally tighten slightly through the 'hitting' zone anyway.  It is an involuntary response (preventing loss of your 'weapon' and preparing for impact) so it is difficult to control entirely.  The natural firming of the grip does has the benefit of maintaining/controlling bat angle through and at impact.  So start relaxed, plan to stay relaxed but don't think about it too much and let nature do the rest.

Can grip tightness be related to my issue against some shots that I feel like the ball is pushing into my bat so hard that it tilts my bat against my power?

Hi DK.  That is probably more perception than reality but if you hold the bat especially loosely and make contact with the ball on the perimeter of the bat instead of the sweet-spot, then it is feasible the force of the ball could cause some minor rotation of the bat in your hand.

You should analyse whether, on those shots, you are making contact in the sweet-spot or not.  Sound and vibration will be your clues. If you are, and still feel the bat is being rotated by the impact of the ball, then think about what Alois suggested above - slightly squeeze your grip as you make contact. Be conscious to do it only on fast incoming balls that you want to also send back fast otherwise you'll get into the habit and it may compromise your technique on other shots, and also your feel.

This mostly happens when I am about to play a flat stroke with my backhand.
Though,it happens even against slow balls that I swing my bat,it hits the ball and in the moment of contact my wrist starts to twist back.
Sometimes I feel like I hit a metal ball.

The fact is that I rarely use sweetspot,though,as I am spin-oriented player and I mostly make contact closer to the leading edge.

Isometimes use the extremely loose grip when I need to dropblock against powerful shot.

Though,I am quite troubled by my pimples on backhand as I do not want to have chopblock only.

Hmm.  Curious.  When it happens on the slow balls, are these also flat hits, or is it also happening on TS/BS shots?

Also, you said your wrist twists back (from the impact?) not just your bat.  This would indicate it isn't your grip allowing this to happen but your wrist.  You can have a relaxed grip but still maintain a firm wrist.  If you have trouble with it though, still try the slight tightening of the grip.  If you use a shake-hand grip try squeezing the handle with the 3 fingers on it.  That will firm up your wrist more than using thumb and index finger pressure and still allow the thumb and index finger to be relaxed to provide the feel and control you want.

Another possibility is to build more grip strength so you can maintain a firmer wrist while still being relaxed.

DK, does this happen if you use shadow play?

Nigel,

well in shadow play there is no ball.
In shadow play I only fell I have very short legs.

Rohan,
It is happening on blocks and flat shots.
Topspin and backspin shots are my dominant game ( I mean strokes with pure rotation and no power).
For example when I try to smash short higher ball (i.e. 40cm) I swing my arm,forearm,wrist-and when I hit the ball,I have the feeling of "blocked tip of the bat",my wrist twists and the ball flies left (with BH) or right (with FH).
That is not affected by incoming spin.
I thought it is caused by my slow bat.,but I tested with various fast bats and I had the same feeling.
Sometimes I even put my back finger (=index finger if FH,thumb if BH) to the middle of the bat to support its face,but still I have a feeling that if I usedmore power,the bat breaks my finger.

DK, Just thought that if it happens when you swing but there is no ball, then obviously it is not the impact that is causing it. On my FH when trying to play a loop if I am not warmed up or if I get nervous then as I hit the ball, the bottom of my blade flips forward and the ball can go straight up! I make sure I warm up before playing. I even start my warm up at home with shadow play. This problem is more like a twitch than being caused by the ball so hopefully it is not like that for you.

I understand you,though during shadow play it does not happen.

I am bad at shadow play as without the bat in hand and table in front of myself,I dont have any way to measure how low I am,distances etc.
Thus if I am doing shadowplay at home,my technique is not improving since it is too unreal or how to describe it.
In other words I must imagine too much and I cannot focus on my movement.

Though,no wrist twisting occurs with no ball.