We'll jump ahead a bit: After the doctors cut off his wetsuit at the hospital, they discovered that the suit was the only thing keeping a good chunk of Fox's insides from being outside. All of his ribs on his left side were broken, his lung was punctured, and the main artery from his heart to his stomach had been exposed.
Thankfully, Fox didn't know that at the time of the attack, so he figured he'd simply poke the shark in the eye and swim away. That seemed to work for a minute, until the shark figured out that a hand is also meat. It took over 90 stitches to repair the damage from that wound. Rapidly running out of ideas, Fox grabbed the shark from behind and held on, reasoning that if he was one with the shark, maybe it wouldn't bite him quite so much. After a few minutes, he realized he'd been underwater for quite some time, and maybe should try to get some air.
After reaching the surface, Fox peered into the water below and saw "this great big shark coming up with its mouth wide open." Then two miraculous things happened. First, the shark went for the fish float attached to Fox's dive belt instead of his delicious soft parts. Second, the line to his belt had been mostly severed by the earlier bite, and thus snapped when the shark snagged his floatie and dived. A passing crew rescued Fox, who later left the hospital with several hundred stitches but no lasting damage. He then went on to swear a lifelong vendetta against marine predators. Or wait, no, he founded an organization to research and protect sharks, because he's a much better person than we are.