The croc was waiting to snag some fish scraps being tossed. A shark tries to fight the croc for the fish & battle ensues
LiveLeak: "Discarded fish scraps attracted the interests of several sharks and a big salt water crocodile. The croc swam up to the boat and waited, ignoring the scraps but had his mouth open and ready. Another scrap was thrown into the water and a shark darted in to claim it, but the croc quickly latched into the shark's head and swam away to a nearby mangrove."