Sun 18-Aug-13 06:22 AM | edited Sun 18-Aug-13 06:23 AM by gfinlayson
If you had taken a lot of photos in quick succession, I expect the camera was probably flushing the full buffer to the memory card. If the buffer is flushing, the memory card access lamp will be lit (see 18 on P5 of the D7100 manual) and the camera will seem unresponsive. The camera also won't turn off until the buffer is empty. Removing the battery at this point will cause data loss and may corrupt the SD card. See P58 of the manual for more details and P348 for information on buffer capacity.