Although Nurse Sharks may appear harmless they can be aggressive and bite. Here's a look at a Nurse Shark bite and treatment thereafter.
Here's an informative video involving a spearfishing shark bite incident that recently occurred in Belize. The video details what precipitated the bite and explains that although nurse sharks may appear harmless, they can become aggressive when searching for food.
On this dive with Captain Shark's Marine Center and Boatyard, one of the divers is bitten on the hand by a nurse shark while spear fishing. It is noted that at the time of the bite, the diver was holding the speargun by the point and the shark most likely confused her hand with a fish.
Following the bite, the video explains how to treat the wound and when to seek further medical assistance.
The video was posted by CaptainSharksBelize and is 4:53 in length. The bite occurs at around the 2:50 mark but I highly recommend watching the complete video as they do an excellent job of pointing out the Do's and Don'ts of diving/fishing in the vicinity of sharks.