Hi John
There are any number of definitions for “firm grip” but they are generally similar to Longmans, apart from the Urban Dictionary. I think if there’s an expression that is in common usage and generally understood, we should use it. Talking about fly casting is difficult enough without adding unnecessary complexity.
Only golf and lifting seem to define grips particularly well, I would class the lifting grips as strong, none of which resemble a fly casting grip that I would expect to see used by competent casters:
https://godsofgrip.com/pages/types-of-grip
The grip in the top photo has rotated a 3 metre rod and a 38 gram line that is 16 or 17 metres long, it was strong enough to achieve that level of performance (whatever the cast measured) but the only way to test the strength of any grip would be to measure it.
I think that we do exercise a firm grip while we overcome the initial torque and relax the grip somewhat when the rod is in motion, whilst torque is reducing and the rod accelerating. After loop formation, we may relax the grip further for damping if required before gripping the budgie to stop it flying away.
A flailing wrist movement will not be achieved when the rod is held tightly and strongly. What you need to do to both optimise and control that flailing movement is to ensure that the rod does not twist away from the casting plane during turnover. How the rod is held in the hand delivers that control.
What I think occurs during flailing movements is that the wrist is stabilised, so that there is no radial or ulnar deviation. This should not overly inhibit flexion/extension, as per a forehand and a backhand slap. This slapping motion should occur as we are relaxing our grip with reducing torque. I think that this is partly how I do short range, long leader/dry fly casts but it does leave me with a large counterflex to deal with, hence my interest in damping.
My post 144 was a bit mischievous in that if you looked at the arms of the casters in isolation, you would not expect to see such light grips. Control of the rod is being exercised with a light touch, while the wrist tendons are prominent, so some effort is being expended somewhere.
Regards
Vince