In terms of self defense, the fingers are individually more vulnerable than the hand. If someone grabs you or is choking you, it is much easier to grab a finger than to pull their hand off, especially the pinkie or ring finger. And typically speaking, break a finger or two, they will likely pull their hand away and give you a moment to strike again.
Here, Captain America - a hero in this film - is standing still while three other kinds of heroes, rush around to do thier job. (this is in no way bashing Cap, he is simply standing still at this moment, most likely in shock/fatigue). A soldier, a BLACK COP and two firemen. While American’s super soldier is immobilized, our every day heroes are still fighting to ensure safety and peace. The fact that Marvel created this moment in thier film, a film focused on the heroes, speaks yet again to thier message that you don’t have to be a super, to be super.