This kind of overscan/underscan thing is not something that many normal consumers will be aware or know about it, and not even every gamers knows that, until this kind of thing has brought to light on eGG Network, where many people complain why the entire picture has been "cropped off".
Currently, eGG Network (ch808) will "underscan" (opposite meaning of overscan) the entire image from their side by around 5% whenever they air any game matches (as shown on picture below), regardless of live broadcasts or repeats.

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As you can see, there's about 5% black bars on the sides, cuz when you underscan, it actually zooms out the actual 100% image.
So if your TV overscans it, it will zoom back in around 5%, so eventually you can see the entire image without cropping. This is what eGG Network is doing.
This is after they received tons of complaints from viewers saying that their TVs set unable to see the sides of the picture (e.g. game scores, map) during the live game match.
At first, many viewers bombard Astro Facebook page, and the customer service representatives also blur blur, don't know what happen. They thought is aspect ratio problem faced by viewers cuz what they heard from customers is "cannot see entire image" or "the sides were cropped off". So they advise viewers to make sure the viewing mode is set to "Fit to screen" by pressing the "aspect ratio/display mode" button (a rectangle shape with square shape inside the rectangle) on Astro remote control. Of course, that advise is not helping at all, LOL. But now you know, it was the overscan problem that occurs on many viewer's TV set, and yet many viewers complained and blamed Astro for that, and then say those not nice words like "I pay you so much money yet you give me this kind of service?".
Of course Astro is being patient with that, since they are already suck a lot of money from customers already.
So, for your info, eGG Network broadcasts in 16:9 aspect ratio only.hahahaha I lost touch with the up and coming DOTA e-players already since the fall of NA'VI from Ukraine in 2013