How do I delete NFL preloaded app,
It's a part of the image, so it won't be able to be deleted. The most you can do is disable it.
To disable:
Go to Settings
Select Applications and select "Application Manager" if prompted.
Scroll to the right to reach the "All Apps" section
Locate the NFL Mobile app and select it.
Click Disable
Click "Yes" to uninstall all updates and disable the app.
You can disable, but not uninstall.