The ring's (at least, the one's like Hal and John got) have a built-in "Protect bearer from mortal harm" function.

It's pretty evident the ring flew onto his hand and allowed him to catch the arrow before it actually hit him. If you look at the panel where you first see the ring, the arrow's not actually in him but is being held between his fingers. The other shots were made to look like it was actually embedded in his chest for suspense and all that other storytelling nonsense. ;)