Nikon D-300

Looks you have a slow memory card. Nothing wrong, when you use class 2, 4 or 6 in your camera, but it will slow things down sometimes. Not only for sports shooting, 5 or more frames a second, you need a fast card. For Video it is advised to chose fast cards to. Some cameras only manage one shot a second, and that will become word, when a slow memory card is in the camera.
I don't say this is the reason, I only say this could be the reason.

nikon r09,r11, etc . it mean memory buffer of your camera. memory buffer is a temporary memory for your captured images before it store to memory card.
if r00 it mean, you can't take a picture, even 1 picture... that because the camera buffer memory is full.
the number of memory buffer will also drop if noise reduction on

i think the frame rate is 1.3 frames per second.

Issue: How do I set Continuous Shooting?
Solution: Setting Continuous Shooting mode PowerShot SD750 and SD1000.

Continuous Shooting In this mode, the camera shoots continuously while the shutter button is held down. Recording ceases when the shutter button is released. In addition, under the following conditions, continuous shooting can occur at a consistent interval until the SD card is full*.

• A resolution and compression combination other than and is selected.
  * If continuous shooting suddenly stops, the SD card may be full.

Continuous shooting is available in all modes except [AUTO], [Stitch Assist], [Color Accent] and [Color Swap].
To set Continuous Shooting

1. Press the button to display .
   
   
   
2. Shoot the image.
   
   The camera will continue to record successive images while the shutter button is fully pressed. Recording will cease when the shutter button is released, the card is full or the card does not support a write speed to allow continuous shooting to continue.

To Cancel Continuous Shooting

1. Press the button twice to display .
   

To enhance the continuous shooting performance when you suspect the speed has dropped, you are recommended to format the SD card in the camera (Low Level Format) after you save all its images to your computer.

• The interval between shots may lengthen slightly when the camera's built-in memory fills.
• If the flash is firing, the interval between shots will lengthen to accommodate the flash's charging requirements.

I am a pro photographer and one of my cameras is an A100. I have noticed this same problem and sometimes when I am shooting fast the shutter delays. I found the problem in my card. My wife bought me a card based on price.  I sugest you use a card that reads faster than the camera can write. You can get the specs on the Sony Camera Site.

First thing to try is new batteries.