I was watching a video about some of the Hiden (Secrets) of Aikijutsu shown by Fredrick J, Lovret.
What I saw in there was use of a grab defense with the index finger held out straight during a counter grab. This was something I had read about written by Dennis Palumbo in his books on training in Hakkou Ryu Jutsu in Japan.
The index finger is held out straight, because the pad of the palm at the index finger is used to press against a point on the opponent’s wrist, and that enables the counter-grab to work and take the opponent down.
Palumbo Sensei also described how being trained on that point in Japan was continually worked. Which led to a bout of diareah. Upon which time the other students then told him that was a common side effect during that training. I never experienced that myself. So I take that part of the story under advisement.
Not long after that I was visiting my friend and mentor, Ernest Rothrock, and we discussed this and spent some time on that movement comparing it to the way the eagle claw is applied against the same grab. Each got an effece. The eagle claw grip using the fingers like pliers digging into the wrist when it was used. The other hand formation using the pressure from the pad of the straight index finger to make it work.
Our conclusion, for the skilled practitioner both work. First he shows how this is used with the straight hand wrist grab.
Then he shows how this is applied against a cross hand wrist grab.
Always time for more work.