Freezing a movement and taking a still image of it is only useful if you can see the movement that came before it and the movement that comes after it.
This image you've given us can be anything, because we can't see what came before and what's coming after it.
If you're assuming that it represents a "fighting stance" or a position that you hold while waiting for something to happen, it may or may not be.
I have seen similar fighting stances from Bujinkan budo taijutsu and other forms of classical jujitsu.
You can look it up on youtube to see some examples.
Just type in "Bujinkan" and scan the video until you see a similar fighting stance.
But given that this picture is of a karate practitioner, that means it's not a fighting stance.
It's a freeze-frame image of the performance of a karate kata.
Find out which kata it's in, which move it occurs on, and then re-post your question asking us to tell you what's going on.
There are many of us that understand karate kata and can give you our analysis.
But it will depend on the context within the kata itself.
The move(s) that came right before it and the move(s) that comes right after it are hugely important.
Hope that helps.
martialarts.stackexchange.com/users/1555/Steve Weigand
It's not a starting position.
It is a defence against a kick.
The rear arm has caught the opponent's leg and it is hooked over it, the front hand is pushing him over backwards.
You would need to see the full sequence of movements in the form to understand how the position is used.
In karate the stance is called "manji-uke" and it has a direct equivalent in Kung-fu.
The application is the same in both cases.
You see this in for example the katas Passai/Bassai Dai, Pinan/Heian Godan and in several kung-fu forms such as Tong Bi Quan.
The sequence in Passai and Tong Bi Quan are the same application.
It's likely that the Passai sequence originated from that or another earlier kung-fu form.
The application in both is: Catch kicking leg and raise it up.
Push opponent over backwards with the other hand.
Step round and kick out his remaining leg, retaining hold of the caught one.
Once opponent is on the ground, use both arms to dislocate/hyperextend the knee joint of the caught leg.
Manji Uke example video created by Iain Abernethy
martialarts.stackexchange.com/users/6808/ColinSeligSmith
Is this a realistic start position in a fight?
No, not at all.
Instead you think of this as a finishing position.
That particular position could be anything, including but not limited to: an arm bar knife hand strike to a nice vulnerable spot (like the neck or the mastoid process) a grapple that is leading to a hammer fist
Personally I never start a fight in a stance or position other than Hachiji dachi ("the ready" stance) - unless the fight starts without me being "ready"!
martialarts.stackexchange.com/users/70/slugster
The picture is used on the cover of Winning Karate by Joseph Jennings.
My guess is that that stance is from some kata, and as such it could be completely reasonable.
But, your critique is of the utility as a general ready stance for fighting, and you're inviting us to join in... As far as that goes
, you're right - it would be terrible if used as a general fighting stance, and it's a good skill to read weaknesses in a position if used during sparring, so here's some analysis: as you say, the back hand is effectively out of play stance is too side on further removing the back hand from play
the back leg is pretty useless too, as it can't take the proper line into a front , side or turning/roundhouse kick
the hips/shoulders have no room left to rotate in behind a front jab the front hand could not comfortably or strongly be brought from his right to left in an inward knife hand or reverse knifehand/ridgehand strike because it'd have to be awkwardly extend outside the line of the shoulders first similarly, the front hand can't strongly block any attack coming in from his blind side, such as an opponent's inward ridgehand, turning/roundhouse kick, spinning heel/hook kick, slapping/crescent kick (soto/uchi mawashi geri)...
the front arm's too straight and out of position
- it would have to be pulled back a long way first before a decent jab or block could be executed
we can't see the leg position, but if the front knee is turned too far inwards, it's especially vulnerable to a stomp at the knee; if it's inline with the shoulders, a low turning/rounding/mawashi-geri forcing it further outward
could be very unpleasant
That said, I have seen some extremely good fighters (e.g. Tsukamoto Norichika of Shin Kyokushin) extend their front arm vaguely similarly when fighting at long distance... perhaps as a way to help gauge distance and perhaps for complex reasons of balance and mobility.
martialarts.stackexchange.com/users/1618/Tony D
I have been known to shift into a fencers stance, similar to this, when I'm playing around in sparring or want to force a student to think differently.
The lead hand is well positioned to parry most attacks to the body and head, including multiple attacks, with little or no movement.
The rear hand helps to maintain balance.
In sparring, it's good for taking a short breather while the clock is running, against a less skilled partner.
Depending on the stance and leg position, it it possible to throw a decent jab, provided it is powered almost entirely by the legs.
This would be more like a fencers lunge than a classical karate or boxing jab.
Some aikido schools use a similar stance to invite certain types of attacks as a setup for a throw.
martialarts.stackexchange.com/users/6599/pojo-guy
Here is a position that I found in some places:    Is this a realistic start position in a fight? Can he use the back hand in this position fast? Isn't it better to position the back hand near the chest in a position that will enable a faster response? Where this position can be used and in what methods?
Is the following position realistic in any fight?
martialarts.stackexchange.com
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martialarts.stackexchange.com/questions/6087
martialarts.stackexchange.com/users/6750/Avi
It is a defence against a kick.  In karate the stance is called "manji-uke" and it has a direct equivalent in Kung-fu. This position is a defence position used against a kick, and the stance  is known as 'manji-uke' in karate.
This position is a defence position used against a kick and the stance  is known as 'manji-uke' in karate.