On MLB.tv there is a setting for the audio to be set to a setting titled "PARK"
Essentially this audio setting features the video of the broadcast of your choice but as for the audio, you listen to an on-field microphone.
It's a good tool if something happens at the plate (like this) where you want to listen in.
How do I find this setting? That'd be great to hear some things that are said on field. I found the video but I only have the option of turning the volume up or down.
When in the MLB.tv browser, On the left hand side of the time bar will be an option, click that. You will then be able to select audio and video options depending on what is provided. Sometimes it's not provided.